Method of improving fast-chargeability of a lithium battery

ABSTRACT

Provided is method of improving fast-chargeability of a lithium secondary battery, wherein the method comprises disposing a lithium ion reservoir between an anode and a porous separator and configured to receive lithium ions from the cathode through the porous separator when the battery is charged and to enable the lithium ions to enter the anode in a time-delayed manner. In some embodiments, the reservoir comprises a conducting porous framework structure having pores and lithium-capturing groups residing in the pores, wherein the lithium-capturing groups are selected from (a) redox forming species that reversibly form a redox pair with a lithium ion; (b) electron-donating groups interspaced between non-electron-donating groups; (c) anions and cations wherein the anions are more mobile than the cations; or (d) chemical reducing groups that partially reduce lithium ions from Li +1  to Li +δ , wherein 0&lt;δ&lt;1.

FIELD OF THE INVENTION

The present invention provides a fast-chargeable lithium-ion battery anda lithium metal battery (having lithium metal or metal alloy as the mainanode active material).

BACKGROUND

Rechargeable lithium-ion (Li-ion) and rechargeable lithium metalbatteries (e.g. lithium-sulfur, lithium-selenium, and Li metal-airbatteries) are considered promising power sources for electric vehicle(EV), hybrid electric vehicle (HEV), and portable electronic devices,such as lap-top computers and mobile phones. Lithium as a metal elementhas the highest lithium storage capacity (3,861 mAh/g) compared to anyother metal or lithium intercalation compound as an anode activematerial (except Li_(4.4)Si, which has a specific capacity of 4,200mAh/g). Hence, in general, Li metal batteries (having a lithium metalanode) have a significantly higher energy density than lithium-ionbatteries (e.g. having a graphite anode).

Historically, rechargeable lithium metal batteries were produced usingnon-lithiated compounds having relatively high specific capacities, suchas TiS₂, MoS₂, MnO₂, CoO₂, and V₂O₅, as the cathode active materials,which were coupled with a lithium metal anode. When the battery wasdischarged, lithium ions were transferred from the lithium metal anodeto the cathode through the electrolyte and the cathode became lithiated.Unfortunately, upon repeated charges and discharges, the lithium metalresulted in the formation of dendrites at the anode that ultimatelycaused internal shorting, thermal runaway, and explosion. As a result ofa series of accidents associated with this problem, the production ofthese types of secondary batteries was stopped in the early 1990'sgiving ways to lithium-ion batteries.

Even now, cycling stability and safety concerns remain the primaryfactors preventing the further commercialization of Li metal batteries(e.g. Lithium-sulfur and Lithium-transition metal oxide cells) for EV,HEV, and microelectronic device applications. Again, cycling stabilityand safety issues of lithium metal rechargeable batteries are primarilyrelated to the high tendency for Li metal to form dendrite structuresduring repeated charge-discharge cycles or overcharges, leading tointernal electrical shorting and thermal runaway. This thermal runawayor even explosion is caused by the organic liquid solvents used in theelectrolyte (e.g. carbonate and ether families of solvents), which areunfortunately highly volatile and flammable.

Many attempts have been made to address the dendrite and thermal runawayissues. However, despite these earlier efforts, no rechargeable Li metalbatteries have succeeded in the market place. This is likely due to thenotion that these prior art approaches still have major deficiencies.For instance, in several cases, the anode or electrolyte structuresdesigned for prevention of dendrites are too complex. In others, thematerials are too costly or the processes for making these materials aretoo laborious or difficult. In most of the lithium metal cells andlithium-ion cells, the electrolyte solvents are flammable. An urgentneed exists for a simpler, more cost-effective, and easier to implementapproach to preventing Li metal dendrite-induced internal short circuitand thermal runaway problems in Li metal batteries and otherrechargeable lithium batteries.

These concerns over the safety of earlier lithium metal secondarybatteries led to the development of lithium-ion batteries, in which purelithium metal sheet or film was replaced by carbonaceous materials (e.g.natural graphite particles) as the anode active material. Thecarbonaceous material absorbs lithium (through intercalation of lithiumions or atoms between graphene planes, for instance) and desorbs lithiumions during the re-charge and discharge phases, respectively, of thelithium-ion battery operation. The carbonaceous material may compriseprimarily graphite that can be intercalated with lithium and theresulting graphite intercalation compound may be expressed as Li_(x)C₆,where x is typically less than 1.

Although lithium-ion (Li-ion) batteries are promising energy storagedevices for electric drive vehicles, state-of-the-art Li-ion batterieshave yet to meet the cost, safety, and performance targets. Li-ion cellstypically use a lithium transition-metal oxide or phosphate as apositive electrode (cathode) that de/re-intercalates Li⁺ at a highpotential with respect to the carbon negative electrode (anode). Thespecific capacity of lithium transition-metal oxide or phosphate basedcathode active material is typically in the range from 140-170 mAh/g. Asa result, the specific energy of commercially available Li-ion cells istypically in the range from 120-220 Wh/kg, most typically 150-180 Wh/kg.These specific energy values are two to three times lower than whatwould be required for battery-powered electric vehicles to be widelyaccepted.

Furthermore, the same flammable solvents previously used for lithiummetal secondary batteries are also used in most of the lithium-ionbatteries. Despite the notion that there is significantly reducedpropensity of forming dendrites in a lithium-ion cell (relative to alithium metal cell), the lithium-ion cell has its own intrinsic safetyissue. For instance, the transition metal elements in the lithium metaloxide cathode are highly active catalysts that can promote andaccelerate the decomposition of organic solvents, causing thermalrunaway or explosion initiation to occur at a relatively low electrolytetemperature (e.g. <200° C., as opposed to normally >400° C. without thecatalytic effect).

Ionic liquids (ILs) are a new class of purely ionic, salt-like materialsthat are liquid at unusually low temperatures. The official definitionof ILs uses the boiling point of water as a point of reference: “Ionicliquids are ionic compounds which are liquid below 100° C.”. Aparticularly useful and scientifically interesting class of ILs is theroom temperature ionic liquid (RTIL), which refers to the ionic saltsthat are liquid at room temperature or below. RTILs are also referred toas organic liquid salts or organic molten salts. An accepted definitionof an RTIL is any salt that has a melting temperature lower than ambienttemperature.

Although ILs were suggested as a potential electrolyte for rechargeablelithium batteries due to their non-flammability, conventional ionicliquid compositions have not exhibited satisfactory performance whenused as an electrolyte likely due to several inherent drawbacks: (a) ILshave relatively high viscosity at room or lower temperatures; thus beingconsidered as not amenable to lithium ion transport; (b) For Li—S celluses, ILs are capable of dissolving lithium polysulfides at the cathodeand allowing the dissolved species to migrate to the anode (i.e., theshuttle effect remains severe); and (c) For lithium metal secondarycells, most of the ILs strongly react with lithium metal at the anode,continuing to consume Li and deplete the electrolyte itself as chargesand discharges are repeated. These factors lead to relatively poorspecific capacity (particularly under high current or highcharge/discharge rate conditions, hence lower power density), lowspecific energy density, rapid capacity decay and poor cycle life.Furthermore, ILs remain extremely expensive. Consequently, as of today,no commercially available lithium battery makes use of an ionic liquidas the primary electrolyte component.

With the rapid development of hybrid (HEV), plug-in hybrid electricvehicles (HEV), and all-battery electric vehicles (EV), there is anurgent need for anode and cathode materials and electrolytes thatprovide a rechargeable battery with a significantly higher specificenergy, higher energy density, higher rate capability, long cycle life,and safety. One of the most promising energy storage devices is thelithium-sulfur (Li—S) cell since the theoretical capacity of Li is 3,861mAh/g and that of S is 1,675 mAh/g. In its simplest form, a Li—S cellconsists of elemental sulfur as the positive electrode and lithium asthe negative electrode. The lithium-sulfur cell operates with a redoxcouple, described by the reaction S₈+16Li↔8Li₂S that lies near 2.2 Vwith respect to Li⁺/Li^(o). This electrochemical potential isapproximately ⅔ of that exhibited by conventional positive electrodes.However, this shortcoming is offset by the very high theoreticalcapacities of both Li and S. Thus, compared with conventionalintercalation-based Li-ion batteries, Li—S cells have the opportunity toprovide a significantly higher energy density (a product of capacity andvoltage). Values can approach 2,500 Wh/kg or 2,800 Wh/l based on thecombined Li and S weight or volume (not based on the total cell weightor volume), respectively, assuming complete reaction to Li₂S. With aproper cell design, a cell-level specific energy of 1,200 Wh/kg (of cellweight) and cell-level energy density of 1,400 Wh/l (of cell volume)should be achievable. However, the current Li-sulfur experimental cellsof industry leaders in sulfur cathode technology have a maximum cellspecific energy of 250-400 Wh/kg (based on the total cell weight), farless than what could be obtained in real practice.

In summary, despite its considerable advantages, the rechargeablelithium metal cell in general and the Li—S cell and the Li-Air cell inparticular are plagued with several major technical problems that havehindered its widespread commercialization:

-   (1) Conventional lithium metal secondary cells (e.g., rechargeable    Li metal cells, Li—S cells, and Li-Air cells) still have dendrite    formation and related internal shorting and thermal runaway issues.    Also, conventional Li-ion cells still make use of significant    amounts of flammable liquids (e.g. propylene carbonate, ethylene    carbonate, 1,3-dioxolane, etc.) as the primary electrolyte solvent,    risking danger of explosion;-   (2) The tendency for a lithium metal anode to form dendrites is    presumably caused by the low deposition rate of the returning    lithium ions onto the Cu foil current collector (and the metal film    previously deposited thereon) during the recharge step. This also    implies that a lithium metal cell cannot be recharged rapidly;-   (3) The Li—S cell tends to exhibit significant capacity degradation    during discharge-charge cycling. This is mainly due to the high    solubility of the lithium polysulfide anions formed as reaction    intermediates during both discharge and charge processes in the    polar organic solvents used in electrolytes. During cycling, the    lithium polysulfide anions can migrate through the separator and    electrolyte to the Li negative electrode whereupon they are reduced    to solid precipitates (Li₂S₂ and/or Li₂S), causing active mass loss.    In addition, the solid product that precipitates on the surface of    the positive electrode during discharge can become electrochemically    irreversible, which also contributes to active mass loss.

More generally speaking, a significant drawback with cells containingcathodes comprising elemental sulfur, organosulfur and carbon-sulfurmaterials relates to the dissolution and excessive out-diffusion ofsoluble sulfides, polysulfides, organo-sulfides, carbon-sulfides and/orcarbon-polysulfides (hereinafter referred to as anionic reductionproducts) from the cathode into the rest of the cell. This phenomenon iscommonly referred to as the Shuttle Effect. This process leads toseveral problems: high self-discharge rates, loss of cathode capacity,corrosion of current collectors and electrical leads resulting in lossof electrical contact to active cell components, fouling of the anodesurface giving rise to malfunction of the anode, and clogging of thepores in the cell membrane separator which leads to loss of iontransport and large increases in internal resistance in the cell.

In response to these challenges, new electrolytes, protective films forthe lithium anode, and solid electrolytes have been developed. Someinteresting cathode developments have been reported recently to containlithium polysulfides; but, their performance still fall short of what isrequired for practical applications. Despite the various approachesproposed for the fabrication of high energy density rechargeable cellscontaining elemental sulfur, organo-sulfur and carbon-sulfur cathodematerials, or derivatives and combinations thereof, there remains a needfor materials and cell designs that (a) retard or reduce theout-diffusion of anionic reduction products, from the cathodecompartments into other components in these cells, (b) improve thebattery safety, and (c) provide rechargeable cells with high capacitiesover a large number of cycles.

Although solid electrolytes are effective in addressing the lithiummetal dendrite and flammability issues, conventional solid-stateelectrolytes have the following major deficiencies: low lithium ionconductivities (typically <<10⁻⁴ S/cm, more typically <<10⁻⁵ S/cm, andfurther more typically <<10⁻⁶ S/cm), difficulty in making solid-stateelectrolyte (high temperature sintering typically required) andimplementing it in a battery cell, extreme brittleness, no flexibility(hence, not being compliant and being in poor ionic contact with theanode and/or cathode and, hence, poor active material utilizationefficiency), and high costs. The low lithium ion conductivity

A specific object of the present invention is to provide a lithium-ionbattery or rechargeable lithium metal battery (e.g. Li—S battery) thatcan be rapidly recharged and exhibits a high specific energy, a longcycle-life, and a high level of safety.

A very important object of the present invention is to provide a simple,cost-effective, and easy-to-implement approach to preventing potentialLi metal dendrite-induced internal short circuit and thermal runawayproblems in various fast-charging Li metal and Li-ion batteries.

SUMMARY OF THE INVENTION

The present invention provides a lithium secondary battery, asschematically illustrated in FIG. 1, comprising an anode, a cathode, aporous separator disposed between the anode and the cathode, anelectrolyte, and a lithium ion reservoir disposed between the anode andthe porous separator and configured to receive lithium ions from thecathode through the porous separator when the battery is charged andenable the lithium ions to enter the anode in a time-delayed manner,wherein the lithium ion reservoir comprises an electron-conductingand/or lithium ion-conducting porous framework structure having pores,having a pore size from 1 nm to 500 μm, and lithium-capturing groupsresiding in the pores, wherein the lithium-capturing groups are selectedfrom (a) redox forming species that reversibly form a redox pair with alithium ion when said battery is charged; (b) electron-donating groupsinterspaced between non-electron-donating groups; (c) anions and cationswherein the anions are more mobile than the cations; or (d) chemicalreducing groups that partially reduce lithium ions from Li⁺¹ to Li^(+δ),wherein 0<δ<1.

The lithium secondary battery can be a lithium-ion battery wherein theanode contains particles of graphite, Si, SiO_(x), Sn, SnO₂, Ge, etc. asthe main anode active material. The battery may be a rechargeablelithium metal battery, such as a lithium-sulfur battery, alithium-selenium battery, or a lithium-air battery, wherein the anodecontains lithium metal (e.g. Li foil) or lithium metal alloy (containingat least 60% by weight of Li element).

The present invention also provides a method of improvingfast-chargeability of a lithium secondary battery containing an anode, acathode, a porous separator disposed between the anode and the cathode,and an electrolyte, wherein the method comprises disposing a lithium ionreservoir between the anode and the porous separator and configured toreceive lithium ions from the cathode through the porous separator whenthe battery is charged and to enable the lithium ions to enter the anodein a time-delayed manner.

In the method, the lithium ion reservoir may comprise anelectron-conducting or lithium ion-conducting porous framework structurehaving pores, having a pore size from 1 nm to 500 μm, andlithium-capturing groups residing in the pores, wherein thelithium-capturing groups are selected from (a) redox forming speciesthat reversibly form a redox pair with a lithium ion when the battery ischarged; (b) electron-donating groups interspaced betweennon-electron-donating groups; (c) anions and cations wherein the anionsare more mobile than the cations; or (d) chemical reducing groups thatpartially reduce lithium ions from Li⁺¹ to Li^(+δ), wherein 0<δ<1.

In certain embodiments, the lithium ion reservoir comprises an ionicliquid hosted by a porous structure.

In some embodiments, the lithium-capturing group is selected from amolecule having a core or backbone structure and at least a side groupthat is ionic or electron rich. The core or backbone structure maycontain an aryl, heterocycloalkyl, crown etheryl, cyclamyl, cyclenyl,1,4,7-triazacyclononayl, hexacyclenyl, cryptandyl, naphtalenyl,antracenyl, phenantrenyl, tetracenyl, chrysenyl, tryphenylenyl, pyrenyl,pentacenyl, single-benzene or cyclic structure, double-benzene orbi-cyclic structure, or multiple-cyclic structure having 3-10 benzenerings.

The side group may contain CO₂H, CO₂M¹, CO₂R, SO₃H, SO₃M¹, PO₃H₂, PO₃M¹₂, PO₃M¹H, PO₄H₂, PO₄M′₂, PO₄M¹H, PO₄M², C(O)NHOH, NH₂, NHR, N(R)₂, NO₂,COOR, CHO, CH₂OH, OH, OR, SH, SR, C(O)N(R)₂, C(O)NHR, C(O)NH₂, halide,tosylate, mesylate, SO₂NHR, triflate, isocyanate, cyanate, thiocyanate,isothiocyanate, R, cyano, CF₃, or Si(OR)₃; wherein R is independentlyselected from methyl, ethyl, isopropyl, n-propyl, alkyl, haloalkyl,cycloalkyl, heterocycloalkyl, aryl, or benzyl; M¹ is selected from Li,Na, K, Rb, or Cs; and M² is selected from Be, Mg, Ca, Sr, or Ba. Theseside groups, when attached to a cyclic core/backbone structure having1-5 benzene rings, appear to be capable of partially or tentativelyreducing lithium ions in the reservoir from Li⁺¹ to Li^(−δ), wherein0<δ<1.

In some specific embodiments, the redox pair with lithium is selectedfrom lithium 4-methylbenzenesulfonate, lithium3,5-dicarboxybenzenesulfonate, lithium2,6-dimethylbenzene-1,4-disulfonate,3,3′-((1,2-dithiane-4,5-diyl)bis(oxy))bis(N-hydroxypropanamide),3,3′-((4-mercapto-1,2-phenylene)bis(oxy))bis(N-hydroxypropanamide),lithium aniline sulfonate, poly(lithium-4-styrenesulfonate, lithiumsulfate, lithium phosphate, lithium phosphate monobasic, lithiumtrifluoromethanesulfonate, lithium1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorooctane-1-sulfonate,lithium 2,6-di-tert-butylbenzene-1,4-disulfonate, lithium anilinesulfonate (wherein the sulfonate may be in any of para, meta and orthopositions), poly(lithium-4-styrenesulfonate, or a combination thereof.

Electron-donating groups may be selected from those molecules having oneto 10 benzene rings or cyclic structure as the core/backbone portionhaving conjugated double bonds, acidic groups, etc. Examples includesodium 4-methylbenzenesulfonate, sodium 3,5-dicarboxybenzenesulfonate,sodium 2,6-dimethylbenzene-1,4-disulfonate, and sodium anilinesulfonate. These molecules in the lithium ion reservoir appear to becapable of partially reducing the incoming lithium ions that passthrough the porous separator from the cathode.

The lithium ion-capturing group may contain a salt that is dissociatedinto an anion and a cation in a liquid medium (typically an organicsolvent). Non-limiting examples of these salts are Li₂CO₃, Li₂O,Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂,Li₂S, Li_(x)SO_(y), Na₂CO₃, Na₂O, Na₂C₂O₄, NaOH, NaX, ROCO₂Na, HCONa,RONa, (ROCO₂Na)₂, (CH₂OCO₂Na)₂, Na₂S, Na_(x)SO_(y), or a combinationthereof, wherein X=F, Cl, I, or Br, R=a hydrocarbon group, 0<x≤1, 1≤y≤4.The liquid medium to dissolve these salts may contain a solvent selectedfrom 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), tetraethyleneglycol dimethylether (TEGDME), poly(ethylene glycol) dimethyl ether(PEGDME), diethylene glycol dibutyl ether (DEGDBE), 2-ethoxyethyl ether(EEE), sulfone, sulfolane, ethylene carbonate (EC), dimethyl carbonate(DMC), methylethyl carbonate (MEC), diethyl carbonate (DEC), ethylpropionate, methyl propionate, propylene carbonate (PC),gamma-butyrolactone (γ-BL), acetonitrile (AN), ethyl acetate (EA),propyl formate (PF), methyl formate (MF), toluene, xylene, methylacetate (MA), fluoroethylene carbonate (FEC), vinylene carbonate (VC),allyl ethyl carbonate (AEC), a hydrofluoroether, hydrofluoro ether(HFE), trifluoro propylene carbonate (FPC), methyl nonafluorobutyl ether(MFE), fluoroethylene carbonate (FEC), tris(trimethylsilyl)phosphite(TTSPi), triallyl phosphate (TAP), ethylene sulfate (DTD), 1,3-propanesultone (PS), propene sultone (PES), diethyl carbonate (DEC),alkylsiloxane (Si—O), alkylsilane (Si—C), liquid oligomeric silaxane(—Si—O—Si—), tetraethylene glycol dimethylether (TEGDME), an ionicliquid solvent, or a combination thereof.

The lithium ion-capturing groups may contain ionic liquids, which arelow melting temperature salts that are in a molten or liquid state whenabove a desired temperature. For instance, a salt is considered as anionic liquid if its melting point is below 100° C. If the meltingtemperature is equal to or lower than room temperature (25° C.), thesalt is referred to as a room temperature ionic liquid (RTIL). Thedesired ionic liquids for use in the presently invented lithium ionreservoir preferably have a melting point lower than 60° C., morepreferably lower than 0° C., and further more preferably lower than −20°C. The IL salts are characterized by weak interactions, due to thecombination of a large cation and a charge-delocalized anion. Thisresults in a low tendency to crystallize due to flexibility (anion) andasymmetry (cation). The anions of the ionic liquid may be selected to bemore mobile than the cations.

A typical and well-known ionic liquid is formed by the combination of a1-ethyl-3-methylimidazolium (EMI) cation and anN,N-bis(trifluoromethane)sulfonamide (TFSI) anion. This combinationgives a fluid with an ionic conductivity comparable to many organicelectrolyte solutions and a low decomposition propensity and low vaporpressure up to ˜300-400° C. This implies a generally low volatility andnon-flammability and, hence, a much safer electrolyte for batteries.

Ionic liquids are basically composed of organic ions that come in anessentially unlimited number of structural variations owing to thepreparation ease of a large variety of their components. Thus, variouskinds of salts can be used to design the ionic liquid that has thedesired properties for a given application. These include, among others,imidazolium, pyrrolidinium and quaternary ammonium salts as cations andbis(trifluoromethanesulfonyl) imide, bis(fluorosulfonyl)imide, andhexafluorophosphate as anions. Based on their compositions, ionicliquids come in different classes that basically include aprotic, proticand zwitterionic types, each one suitable for a specific application.

Common cations of room temperature ionic liquids (RTILs) include, butnot limited to, tetraalkylammonium, di-, tri-, andtetra-alkylimidazolium, alkylpyridinium, dialkyl-pyrrolidinium,dialkylpiperidinium, tetraalkylphosphonium, and trialkylsulfonium.Common anions of RTILs include, but not limited to, BF₄ ⁻, B(CN)₄ ⁻,CH₃BF₃ ⁻, CH2CHBF₃ ⁻, CF₃BF₃ ⁻, C₂F₅BF₃ ⁻, n-C₃F₇BF₃ ⁻, n-C₄F₉BF₃ ⁻, PF₆⁻, CF₃CO₂ ⁻, CF₃SO₃ ⁻, N(SO₂CF₃)₂ ⁻, N(COCF₃)(SO₂CF₃)⁻, N(SO₂F)₂ ⁻,N(CN)₂ ⁻, C(CN)₃ ⁻, SCN⁻, SeCN⁻, CuCl₂ ⁻, AlCl₄ ⁻, F(HF)₂₃, etc.Relatively speaking, the combination of imidazolium- or sulfonium-basedcations and complex halide anions such as AlCl₄ ⁻, BF₄ ⁻, CF₃CO₂ ⁻,CF₃SO₃ ⁻, NTf₂ ⁻, N(SO₂F)₂ ⁻, or F(HF)_(2.3) ⁻ results in RTILs withgood working conductivities.

During the battery recharging step, the porous framework structure isconfigured to receive lithium ions coming from the cathode through theporous separator and tentatively or partially retain the lithium ions(not lithium metal) in the pores of this lithium ion reservoir,typically a thin layer between the anode and the separator. This thinlayer of lithium ion reservoir preferably has a thickness from 10 nm to500 μm, more preferably from 100 nm to 100 μm. This lithium ionreservoir may further contain some electrolyte (e.g. liquidelectrolyte).

In some embodiments, the porous framework structure contains aconducting foam, which can be a closed-cell foam or open-cell foam. Theopen-cell foam is preferred. However, the pores preferably containmesoscaled pores having a pore size from 2 nm to 100 nm, more preferablyfrom 2 nm to 50 nm, which are more effective in holding certain lithiumion-capturing species.

In some embodiments, the electron-conducting porous structure has porewalls comprising an electron-conducting material selected from carbonnanotubes, carbon nanofibers, graphene sheets, expanded graphiteplatelets, carbon fibers, graphite fibers, graphite particles, needlecoke, mesocarbon microbeads, carbon particles, carbon black, acetyleneblack, activated carbon particles, or a combination thereof. Multiplefibers or particles of electron-conducting materials optionally may bebonded by a resin binder (0.1%-10%) to improve the structural integrityof the porous structure. Preferably, the electron-conducting porousstructure contains a graphene foam.

In certain embodiments, the lithium ion-conducting porous structurecomprises a polymer foam or polymer fabric having pores and pore walls.The pore walls comprise a lithium ion-conducting polymer having alithium ion conductivity from 10⁻⁸ to 10⁻² S/cm when measured at 25° C.The polymer foam may contain some desired amount of anelectron-conducting material selected from, for instance, carbonnanotubes, carbon nanofibers, graphene sheets, expanded graphiteplatelets, carbon fibers, graphite fibers, graphite particles, needlecoke, mesocarbon microbeads, carbon particles, carbon black, acetyleneblack, activated carbon particles, or a combination thereof.

In some embodiments, the lithium ion-conducting polymer is selected fromsulfonated polyaniline, sulfonated polypyrrole, a sulfonatedpolythiophene, sulfonated polyfuran, a sulfonated bi-cyclic polymer, ora combination thereof.

In some embodiments, the lithium ion-conducting polymer is selected fromsulfonated natural polyisoprene, sulfonated synthetic polyisoprene,sulfonated polybutadiene, sulfonated chloroprene rubber, sulfonatedpolychloroprene, sulfonated butyl rubber, sulfonated styrene-butadienerubber, sulfonated nitrile rubber, sulfonated ethylene propylene rubber,sulfonated ethylene propylene diene rubber, metallocene-based sulfonatedpoly(ethylene-co-octene) elastomer, sulfonated poly(ethylene-co-butene)elastomer, sulfonated styrene-ethylene-butadiene-styrene elastomer,sulfonated epichlorohydrin rubber, sulfonated polyacrylic rubber,sulfonated silicone rubber, sulfonated fluorosilicone rubber, sulfonatedperfluoroelastomers, sulfonated polyether block amides, sulfonatedchlorosulfonated polyethylene, sulfonated ethylene-vinyl acetate,sulfonated thermoplastic elastomer, sulfonated protein resilin,sulfonated protein elastin, sulfonated ethylene oxide-epichlorohydrincopolymer, sulfonated polyurethane, sulfonated urethane-urea copolymer,or a combination thereof.

In some embodiments, the lithium ion-conducting polymer is selected fromthe group consisting of poly(perfluoro sulfonic acid), sulfonatedpolytetrafluoroethylene, sulfonated perfluoroalkoxy derivatives ofpolytetra-fluoroethylene, sulfonated polysulfone, sulfonated poly(etherketone), sulfonated poly (ether ether ketone), sulfonated polystyrene,sulfonated polyimide, sulfonated styrene-butadiene copolymers,sulfonated poly chloro-trifluoroethylene, sulfonatedperfluoroethylene-propylene copolymer, sulfonatedethylene-chlorotrifluoroethylene copolymer, sulfonatedpolyvinylidenefluoride, sulfonated copolymers of polyvinylidenefluoridewith hexafluoropropene and tetrafluoroethylene, sulfonated copolymers ofethylene and tetrafluoroethylene, polybenzimidazole, and chemicalderivatives, copolymers, and blends thereof.

In some embodiments, the lithium ion-conducting polymer is selected frompoly(ethylene oxide) (PEO), polypropylene oxide (PPO),poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA),poly(vinylidene fluoride) (PVDF), poly bis-methoxyethoxyethoxide-phosphazene, polyvinyl chloride, polydimethylsiloxane,and poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP) copolymer,modified polyacrylic acid-based copolymer, polyester polyamineamide-based copolymer, polycarboxylic acid-based copolymer, polyalkylolamino amide-based copolymer, polysiloxane polyacryl-based copolymer,polysiloxane polycarboxylic acid-based copolymer, polyalkoxylate-basedcopolymer, a copolymer of polyacryl and polyether, a derivative thereof,or a combination thereof.

In the lithium-ion battery, the anode (sometimes referred to as anodeelectrode) typically is composed of an anode active material, aconductive additive (e.g. carbon black, acetylene black, graphiteplatelets, carbon nanotubes, etc.), and a resin binder (e.g. thewell-known SBR rubber, PVDF, CMC, etc.). In some embodiments, the anodeelectrode may comprise an anode active material comprising an elementselected from Si, Ge, Sn, Cd, Sb, Pb, Bi, Zn, Al, Co, Ni, Ti, or analloy thereof.

In some embodiments, the anode comprises an anode active materialselected from the group consisting of:

-   -   a) lithiated and un-lithiated silicon (Si), germanium (Ge), tin        (Sn), lead (Pb), antimony (Sb), bismuth (Bi), zinc (Zn),        aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), and        cadmium (Cd);    -   b) lithiated and un-lithiated alloys or intermetallic compounds        of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co, or Cd with other        elements;    -   c) lithiated and un-lithiated oxides, carbides, nitrides,        sulfides, phosphides, selenides, and tellurides of Si, Ge, Sn,        Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, Mn, V, or Cd, and their        mixtures, composites, or lithium-containing composites;    -   d) lithiated and un-lithiated salts and hydroxides of Sn;    -   e) lithium titanate, lithium manganate, lithium aluminate,        lithium-containing titanium oxide, lithium transition metal        oxide;    -   f) lithiated and un-lithiated particles of natural graphite,        artificial graphite, mesocarbon microbeads, hard carbon        (commonly defined as the carbon materials that cannot be        graphitized at a temperature higher than 2,500° C.), soft carbon        (carbon materials that can be graphitized at a temperature        higher than 2,500° C.), needle coke, polymeric carbon, carbon or        graphite fiber segments, carbon nanofiber or graphitic        nanofiber, carbon nanotube;    -   and combinations thereof.

The particles of an anode active material (e.g. Si, Ge, SiO_(x), Sn,SnO₂, etc., wherein x=0.01-1.9) preferably have a diameter from 10 nm to1 μm, more preferably from 20 to 500 nm, and most preferably from 20 to100 nm.

The electrolyte used in the instant lithium battery may be selected froma non-aqueous liquid electrolyte, polymer gel electrolyte, polymerelectrolyte, quasi-solid electrolyte, solid-state inorganic electrolyte,ionic liquid electrolyte, or a combination thereof.

In certain embodiments, the electrolyte comprises a lithiumion-conducting inorganic species or lithium salt selected from lithiumperchlorate LiClO₄, lithium hexafluorophosphate LiPF₆, lithiumborofluoride LiBF₄, lithium hexafluoroarsenide LiAsF₆, lithiumtrifluoro-metasulfonate LiCF₃SO₃, bis-trifluoromethyl sulfonylimidelithium LiN(CF₃SO₂)₂, lithium bis(oxalato)borate LiBOB, lithiumoxalyldifluoroborate LiBF₂C₂O₄, lithium oxalyldifluoroborate LiBF₂C₂O₄,lithium nitrate LiNO₃, Li-fluoroalkyl-phosphates LiPF₃(CF₂CF₃)₃, lithiumbisperfluoro-ethysulfonylimide LiBETI, lithiumbis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide,lithium trifluoromethanesulfonimide LiTFSI, an ionic liquid-basedlithium salt, or a combination thereof.

The electrolyte may comprise a solvent selected from 1,3-dioxolane(DOL), 1,2-dimethoxyethane (DME), tetraethylene glycol dimethylether(TEGDME), poly(ethylene glycol) dimethyl ether (PEGDME), diethyleneglycol dibutyl ether (DEGDBE), 2-ethoxyethyl ether (EEE), sulfone,sulfolane, ethylene carbonate (EC), dimethyl carbonate (DMC),methylethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate,methyl propionate, propylene carbonate (PC), gamma-butyrolactone (γ-BL),acetonitrile (AN), ethyl acetate (EA), propyl formate (PF), methylformate (MF), toluene, xylene, methyl acetate (MA), fluoroethylenecarbonate (FEC), vinylene carbonate (VC), allyl ethyl carbonate (AEC), ahydrofluoroether, an ionic liquid solvent, or a combination thereof.

The electrolyte is preferably a non-flammable electrolyte e.g. anelectrolyte having a flash point higher than 150° C., preferably higherthan 200° C., and most preferably no detectable flash point (flash pointbeing too high to be detectable or the amount of organic vapor being toolittle to detect at a temperature as high as 200° C.).

The non-flammable electrolyte can be a room temperature ionic liquid.Alternatively, the non-flammable electrolyte contains a solid polymerelectrolyte or an inorganic solid electrolyte.

In certain embodiments, a non-flammable quasi-solid electrolyte containsa lithium salt dissolved in a liquid solvent having a lithium saltconcentration from 3.5 M to 14.0 M (more typically from 3.5 M to 10 Mand further more typically from 5.0 M to 7.5 M) so that the electrolyteexhibits a vapor pressure less than 0.01 kPa when measured at 20° C., avapor pressure less than 60% of the vapor pressure of the liquid solventalone, a flash point at least 20 degrees Celsius higher than a flashpoint of the liquid solvent alone, a flash point higher than 150° C., orno flash point.

In certain embodiments, a non-flammable quasi-solid electrolyte containsa lithium salt dissolved in a mixture of a liquid solvent and a liquidadditive having a lithium salt concentration from 1.5 M to 5.0 M so thatthe electrolyte exhibits a vapor pressure less than 0.01 kPa whenmeasured at 20° C., a vapor pressure less than 60% of the vapor pressureof the liquid solvent alone, a flash point at least 20 degrees Celsiushigher than a flash point of the liquid solvent alone, a flash pointhigher than 150° C., or no flash point. The liquid additive, differentin composition than the liquid solvent, is selected from hydrofluoroether (HFE), trifluoro propylene carbonate (FPC), methyl nonafluorobutylether (MFE), fluoroethylene carbonate (FEC),tris(trimethylsilyl)phosphite (TTSPi), triallyl phosphate (TAP),ethylene sulfate (DTD), 1,3-propane sultone (PS), propene sultone (PES),diethyl carbonate (DEC), alkylsiloxane (Si—O), alkylsilane (Si—C),liquid oligomeric silaxane (—Si—O—Si—), tetraethylene glycoldimethylether (TEGDME), canola oil, or a combination thereof. The liquidadditive-to-liquid solvent ratio in the mixture is from 5/95 to 95/5 byweight, preferably from 15/85 to 85/15 by weight, further preferablyfrom 25/75 to 75/25 by weight, and most preferably from 35/65 to 65/35by weight.

There is no limitation on the type of cathode active materials that canbe incorporated in the cathode. Any commonly used cathode activematerial for a lithium-ion battery or lithium metal battery can be usedfor practicing the present invention. The cathode active material may beselected from an inorganic material, an organic or polymeric material, ametal oxide, metal phosphate, metal sulfide, metal halide, metalselenide, or a combination thereof.

As some non-limiting examples, the metaloxide/phosphate/sulfide/selenide/halide may be selected from a lithiumcobalt oxide, lithium nickel oxide, lithium manganese oxide, lithiumvanadium oxide, lithium-mixed metal oxide (e.g. the well-known NCM andNCA), lithium iron phosphate, lithium manganese phosphate, lithiumvanadium phosphate, lithium mixed metal phosphate, sodium cobalt oxidesodium nickel oxide, sodium manganese oxide, sodium vanadium oxide,sodium-mixed metal oxide, sodium iron phosphate, sodium manganesephosphate, sodium vanadium phosphate, sodium mixed metal phosphate,transition metal sulfide, lithium polysulfide, sodium polysulfide,lithium selenide, magnesium polysulfide, or a combination thereof.

In some embodiments, the cathode active material is selected fromsulfur, sulfur compound, sulfur-carbon composite, sulfur-polymercomposite, lithium polysulfide, transition metal dichalcogenide, atransition metal trichalcogenide, or a combination thereof. Theinorganic material may be selected from TiS₂, TaS₂, MoS₂, NbSe₃, MnO₂,CoO₂, an iron oxide, a vanadium oxide, or a combination thereof.

In some embodiments, the metal oxide/phosphate/sulfide contains avanadium oxide selected from the group consisting of VO₂, Li_(x)VO₂,V₂O₅, Li_(x)V₂O₅, V₃O₈, Li_(x)V₃O₈, Li_(x)V₃O₇, V₄O₉, Li_(x)V₄O₉, V₆O₁₃,Li_(x)V₆O₁₃, their doped versions, their derivatives, and combinationsthereof, wherein 0.1<x<5. In some embodiments, the metaloxide/phosphate/sulfide is selected from a layered compound LiMO₂,spinel compound LiM₂O₄, olivine compound LiMPO₄, silicate compoundLi₂MSiO₄, Tavorite compound LiMPO₄F, borate compound LiMBO₃, or acombination thereof, wherein M is a transition metal or a mixture ofmultiple transition metals.

The inorganic material for use as a cathode active material may beselected from: (a) bismuth selenide or bismuth telluride, (b) transitionmetal dichalcogenide or trichalcogenide, (c) sulfide, selenide, ortelluride of niobium, zirconium, molybdenum, hafnium, tantalum,tungsten, titanium, cobalt, manganese, iron, nickel, or a transitionmetal; (d) boron nitride, or (e) a combination thereof.

In some embodiments, the organic material or polymeric material isselected from poly(anthraquinonyl sulfide) (PAQS), a lithium oxocarbon,3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),poly(anthraquinonyl sulfide), pyrene-4,5,9,10-tetraone (PYT),polymer-bound PYT, Quino(triazene), redox-active organic material,Tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE),2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), poly(5-amino-1,4-dyhydroxyanthraquinone) (PADAQ), phosphazene disulfide polymer ([(NPS₂)₃]n),lithiated 1,4,5,8-naphthalenetetraol formaldehyde polymer,hexaazatrinaphtylene (HATN), hexaazatriphenylene hexacarbonitrile(HAT(CN)₆), 5-benzylidene hydantoin, isatine lithium salt, pyromelliticdiimide lithium salt, tetrahydroxy-p-benzoquinone derivatives (THQLi₄),N,N′-diphenyl-2,3,5,6-tetraketopiperazine (PHP),N,N′-diallyl-2,3,5,6-tetraketopiperazine (AP),N,N′-dipropyl-2,3,5,6-tetraketopiperazine (PRP), a thioether polymer, aquinone compound, 1,4-benzoquinone, 5,7,12,14-pentacenetetrone (PT),5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ),5-amino-1,4-dyhydroxy anthraquinone (ADAQ), calixquinone, Li₄C₆O₆,Li₂C₆O₆, Li₆C₆O₆, or a combination thereof. These compounds arepreferably mixed with a conducting material to improve their electricalconductivity and rigidity so as to enable the peeling-off of graphenesheets from the graphitic material particles.

The thioether polymer in the above list may be selected frompoly[methanetetryl-tetra(thiomethylene)] (PMTTM),poly(2,4-dithiopentanylene) (PDTP), a polymer containingpoly(ethene-1,1,2,2-tetrathiol) (PETT) as a main-chain thioetherpolymers, a side-chain thioether polymer having a main-chain consistingof conjugating aromatic moieties, and having a thioether side chain as apendant, poly(2-phenyl-1,3-dithiolane) (PPDT),poly(1,4-di(1,3-dithiolan-2-yl)benzene) (PDDTB),poly(tetrahydrobenzodithiophene) (PTHBDT),poly[1,2,4,5-tetrakis(propylthio)benzene] (PTKPTB, orpoly[3,4(ethylenedithio)thiophene] (PEDTT).

In some embodiments, the organic material contains a phthalocyaninecompound selected from copper phthalocyanine, zinc phthalocyanine, tinphthalocyanine, iron phthalocyanine, lead phthalocyanine, nickelphthalocyanine, vanadyl phthalocyanine, fluorochromium phthalocyanine,magnesium phthalocyanine, manganous phthalocyanine, dilithiumphthalocyanine, aluminum phthalocyanine chloride, cadmiumphthalocyanine, chlorogallium phthalocyanine, cobalt phthalocyanine,silver phthalocyanine, a metal-free phthalocyanine, a chemicalderivative thereof, or a combination thereof. These compounds arepreferably mixed with a conducting material to improve their electricalconductivity and rigidity so as to enable the peeling-off of graphenesheets from the graphitic material particles.

The advantages and features of the present invention will become moretransparent with the description of the following best mode practice andillustrative examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) Schematic of a rechargeable lithium metal battery containing alithium metal anode and a lithium ion reservoir disposed between theanode and the porous separator;

FIG. 1(B) Schematic of a lithium-ion battery containing an anode(comprising particles of an anode active material, such as Si and SnO₂,an optional conductive additive, and an optional resin binder) and alithium ion reservoir disposed between the anode and the porousseparator.

FIG. 2 Lithium ion conductivity values in a solid polymer mixture of asulfonated polymer (S-PEEK or S-PTFE) and a conventional electrolytepolymer (PEO or PPO) plotted as a function of the sulfonated polymerproportion (each containing 30% by weight of lithium salt).

FIG. 3 The actual charge storage capacity values of two cells eachcontaining an anode of lithiated natural graphite particles and acathode of GO/Li_(x)V₃O₈ nanosheets are plotted as a function of the Crates. One cell contains a lithium ion reservoir disposed between theanode and the porous separator, but the other cell does not have such areservoir.

FIG. 4 The discharge capacity values of two Li—S cells (each featuring aLi foil as the anode active material and graphene-supported sulfur asthe cathode active material) are plotted as a function of the number ofcharge/discharge cycles. One cell contains a lithium ion reservoirdisposed between the Li metal anode and the separator, but the othercell does not have such a reservoir.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides a safe and high-performing rechargeablelithium battery, which can be any of the various types of lithium-ioncells (e.g. using graphite or Si as the main anode active material) orlithium metal cells (e.g. Li-metal oxide, Li—S, Li-air, and Li—Se cells,etc. using lithium metal as the main anode active material). Forillustration purpose, the following discussion of preferred embodimentsis primarily based on Li-ion cells and Li—S cells (as an example), butthe same or similar principles and procedures are applicable to allother rechargeable lithium metal batteries (using lithium metal or metalalloy as the anode active material). The cathode active materials canbe, for instance, a transition metal oxide (e.g. V₂O₅) or sulfide (e.g.MoS₂), sulfur or polysulfide (e.g. lithium polysulfide), selenium, metalselenide, or just outside air (for a lithium-air cell).

The present invention provides a lithium secondary battery, asschematically illustrated in FIG. 1(A) for a lithium metal battery (e.g.having a lithium metal foil or lithium alloy powder layer as the primaryanode active material) or FIG. 1(B) for a lithium-ion battery (e.g.having a layer of particles of an anode active material, such asgraphite, Si, Ge, Sn, SnO₂, and optional conductive additive and resinbinder). The lithium secondary battery comprises an anode, a cathode, aporous separator disposed between the anode and the cathode, anelectrolyte, and a lithium ion reservoir disposed between the anode andthe porous separator and configured to receive lithium ions from thecathode through the porous separator when the battery is charged andenable the lithium ions to enter the anode in a time-delayed manner. Thelithium ion reservoir comprises an electron-conducting or lithiumion-conducting porous framework structure having pores, having a poresize from 1 nm to 500 μm, and lithium-capturing groups residing in thepores, wherein the lithium-capturing groups are selected from (a) redoxforming species that reversibly form a redox pair with a lithium ionwhen the battery is charged; (b) electron-donating groups interspacedbetween non-electron-donating groups; (c) anions and cations wherein theanions are more mobile than the cations; or (d) chemical reducing groupsthat partially reduce lithium ions from Li⁺¹ to Li^(+δ), wherein 0<δ<1.

The term “in a time-delayed manner” means that (a) at least a portion(e.g. no less than 10%) of the lithium ions that enter the lithium ionreservoir does not immediately enter the anode layer (but being retainedin the reservoir) when the battery is charged at a charging rate of 5 Cor higher; or (b) when the external battery charger is switched off orunplugged, at least a portion of the of the lithium ions that enter thelithium ion reservoir remains in the reservoir and continues to enterthe anode and the anode active material (i.e. the internal chargingprocedure continues even though the external charger is off). Thepresently invented lithium ion reservoir strategy enables the chargingprocess to be conducted in a time-delayed manner to allow most of theavailable lithium ions to eventually get charged into the anode activematerial. Without such a lithium ion reservoir, fast charging can leadto either a significantly lower amount of lithium ions that actually getintercalated or inserted into the anode active material or the formationof lithium metal plating and dangerous lithium dendrite formation.

In some embodiments, the lithium-capturing group is selected from amolecule having a core or backbone structure and at least a side groupthat is ionic or electron-rich in nature. The core or backbone structuremay contain an aryl, heterocycloalkyl, crown etheryl, cyclamyl,cyclenyl, 1,4,7-triazacyclononayl, hexacyclenyl, cryptandyl,naphtalenyl, antracenyl, phenantrenyl, tetracenyl, chrysenyl,tryphenylenyl, pyrenyl, pentacenyl, single-benzene or cyclic structure,double-benzene or bi-cyclic structure, or multiple-cyclic structurehaving 3-10 benzene rings. The side group may contain CO₂H, CO₂M¹, CO₂R,SO₃H, SO₃M¹, PO₃H₂, PO₃M¹ ₂, PO₃M¹H, PO₄H₂, PO₄M′₂, PO₄M¹H, PO₄M²,C(O)NHOH, NH₂, NHR, N(R)₂, NO₂, COOR, CHO, CH₂OH, OH, OR, SH, SR,C(O)N(R)₂, C(O)NHR, C(O)NH₂, halide, tosylate, mesylate, SO₂NHR,triflate, isocyanate, cyanate, thiocyanate, isothiocyanate, R, cyano,CF₃, or Si(OR)₃; wherein R is independently selected from methyl, ethyl,isopropyl, n-propyl, alkyl, haloalkyl, cycloalkyl, heterocycloalkyl,aryl, or benzyl; M¹ is selected from Li, Na, K, Rb, or Cs; M² isselected from Be, Mg, Ca, Sr, or Ba.

In some specific embodiments, the redox pair with lithium is selectedfrom lithium 4-methylbenzenesulfonate, lithium3,5-dicarboxybenzenesulfonate, lithium2,6-dimethylbenzene-1,4-disulfonate,3,3′-((1,2-dithiane-4,5-diyl)bis(oxy))bis(N-hydroxypropanamide),3,3′-((4-mercapto-1,2-phenylene)bis(oxy))bis(N-hydroxypropanamide),lithium aniline sulfonate, poly(lithium-4-styrenesulfonate, lithiumsulfate, lithium phosphate, lithium phosphate monobasic, lithiumtrifluoromethanesulfonate, lithium1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorooctane-1-sulfonate,lithium 2,6-di-tert-butylbenzene-1,4-disulfonate, lithium anilinesulfonate (wherein the sulfonate may be in any of para, meta and orthopositions), poly(lithium-4-styrenesulfonate, or a combination thereof.

Electron-donating groups may be selected from those molecules having oneto 10 benzene rings or cyclic structure as the core/backbone portionhaving conjugated double bonds, acidic groups, etc. Examples includesodium 4-methylbenzenesulfonate, sodium 3,5-dicarboxybenzenesulfonate,sodium 2,6-dimethylbenzene-1,4-disulfonate, and sodium anilinesulfonate. These molecules in the lithium ion reservoir appear to becapable of partially reducing the incoming lithium ions that passthrough the porous separator from the cathode.

The lithium ion-capturing group may contain a salt that is dissociatedinto an anion and a cation in a liquid medium (typically an organicsolvent). Non-limiting examples of these salts are Li₂CO₃, Li₂O,Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂,Li₂S, Li_(x)SO_(y), Na₂CO₃, Na₂O, Na₂C₂O₄, NaOH, NaX, ROCO₂Na, HCONa,RONa, (ROCO₂Na)₂, (CH₂OCO₂Na)₂, Na₂S, Na_(x)SO_(y), or a combinationthereof, wherein X=F, Cl, I, or Br, R=a hydrocarbon group, 0<x<1, I<y<4.The liquid medium to dissolve these salts may contain a solvent selectedfrom 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), tetraethyleneglycol dimethylether (TEGDME), poly(ethylene glycol) dimethyl ether(PEGDME), diethylene glycol dibutyl ether (DEGDBE), 2-ethoxyethyl ether(EEE), sulfone, sulfolane, ethylene carbonate (EC), dimethyl carbonate(DMC), methylethyl carbonate (MEC), diethyl carbonate (DEC), ethylpropionate, methyl propionate, propylene carbonate (PC),gamma-butyrolactone (γ-BL), acetonitrile (AN), ethyl acetate (EA),propyl formate (PF), methyl formate (MF), toluene, xylene, methylacetate (MA), fluoroethylene carbonate (FEC), vinylene carbonate (VC),allyl ethyl carbonate (AEC), a hydrofluoroether, hydrofluoro ether(HFE), trifluoro propylene carbonate (FPC), methyl nonafluorobutyl ether(MFE), fluoroethylene carbonate (FEC), tris(trimethylsilyl)phosphite(TTSPi), triallyl phosphate (TAP), ethylene sulfate (DTD), 1,3-propanesultone (PS), propene sultone (PES), diethyl carbonate (DEC),alkylsiloxane (Si—O), alkylsilane (Si—C), liquid oligomeric silaxane(—Si—O—Si—), tetraethylene glycol dimethylether (TEGDME), an ionicliquid solvent, or a combination thereof.

The lithium ion-capturing groups may contain ionic liquids, which arelow melting temperature salts that are in a molten or liquid state whenabove a desired temperature. For instance, a salt is considered as anionic liquid if its melting point is below 100° C. If the meltingtemperature is equal to or lower than room temperature (25° C.), thesalt is referred to as a room temperature ionic liquid (RTIL). Thedesired ionic liquids for use in the presently invented lithium ionreservoir preferably have a melting point lower than 60° C., morepreferably lower than 0° C., and further more preferably lower than −20°C. The IL salts are characterized by weak interactions, due to thecombination of a large cation and a charge-delocalized anion. Thisresults in a low tendency to crystallize due to flexibility (anion) andasymmetry (cation). The anions of the ionic liquid may be selected to bemore mobile than the cations.

A typical and well-known ionic liquid is formed by the combination of a1-ethyl-3-methylimidazolium (EMI) cation and anN,N-bis(trifluoromethane)sulfonamide (TFSI) anion. This combinationgives a fluid with an ionic conductivity comparable to many organicelectrolyte solutions and a low decomposition propensity and low vaporpressure up to ˜300-400° C. This implies a generally low volatility andnon-flammability and, hence, a much safer electrolyte for batteries.

Ionic liquids are basically composed of organic ions that come in anessentially unlimited number of structural variations owing to thepreparation ease of a large variety of their components. Thus, variouskinds of salts can be used to design the ionic liquid that has thedesired properties for a given application. These include, among others,imidazolium, pyrrolidinium and quaternary ammonium salts as cations andbis(trifluoromethanesulfonyl) imide, bis(fluorosulfonyl)imide, andhexafluorophosphate as anions. Based on their compositions, ionicliquids come in different classes that basically include aprotic, proticand zwitterionic types, each one suitable for a specific application.

Common cations of room temperature ionic liquids (RTILs) include, butnot limited to, tetraalkylammonium, di-, tri-, andtetra-alkylimidazolium, alkylpyridinium, dialkyl-pyrrolidinium,dialkylpiperidinium, tetraalkylphosphonium, and trialkylsulfonium.Common anions of RTILs include, but not limited to, BF₄ ⁻, B(CN)₄ ⁻,CH₃BF₃ ⁻, CH2CHBF₃ ⁻, CF₃BF₃ ⁻, C₂F₅BF₃ ⁻, n-C₃F₇BF₃ ⁻, n-C₄F₉BF₃ ⁻, PF₆⁻, CF₃CO₂ ⁻, CF₃SO₃ ⁻, N(SO₂CF₃)₂ ⁻, N(COCF₃)(SO₂CF₃)⁻, N(SO₂F)₂ ⁻,N(CN)₂ ⁻, C(CN)₃ ⁻, SCN⁻, SeCN⁻, CuCl₂ ⁻, AlCl₄ ⁻, F(HF)₂₃, etc.Relatively speaking, the combination of imidazolium- or sulfonium-basedcations and complex halide anions such as AlCl₄ ⁻, BF₄ ⁻, CF₃CO₂ ⁻,CF₃SO₃ ⁻, NTf₂ ⁻, N(SO₂F)₂ ⁻, or F(HF)₂₃ ⁻ results in RTILs with goodworking conductivities.

In the lithium secondary battery, the pores preferably containmesoscaled pores having a pore size from 2 nm to 100 nm, preferably from2 nm to 50 nm. These mesopores are particularly effective in holding thelithium-capturing groups inside the pores to perform their intendedfunctions.

In some embodiments, the electron-conducting porous structure has porewalls comprising an electron-conducting material selected from carbonnanotubes, carbon nanofibers, graphene sheets, expanded graphiteplatelets, carbon fibers, graphite fibers, graphite particles, needlecoke, mesocarbon microbeads, carbon particles, carbon black, acetyleneblack, activated carbon particles, or a combination thereof. In someembodiments, the electron-conducting material is made into a fabric(woven or non-woven), paper, or foam structure. The foam structure maybe a closed-cell foam, but preferably an open-cell foam. Theconstruction or production of these electron-conducting materials in afabric, paper, or foam structure is well-known in the art.

Preferably, the electron-conducting porous structure contains a graphenefoam. Generally speaking, a foam (or foamed material) is composed ofpores (or cells) and pore walls (the solid portion of a foam material).The pores can be interconnected to form an open-cell foam. A graphenefoam is composed of pores and pore walls that contain a graphenematerial. There are several major methods of producing graphene foams:

The first method is the hydrothermal reduction of graphene oxidehydrogel that typically involves sealing graphene oxide (GO) aqueoussuspension in a high-pressure autoclave and heating the GO suspensionunder a high pressure (tens or hundreds of atm) at a temperaturetypically in the range from 180−300° C. for an extended period of time(typically 12-36 hours). A useful reference for this method is givenhere: Y. Xu, et al. “Self-Assembled Graphene Hydrogel via a One-StepHydrothermal Process,” ACS Nano 2010, 4, 4324-4330.

The second method is based on a template-assisted catalytic CVD process,which involves CVD deposition of graphene on a sacrificial template(e.g. Ni foam). The graphene material conforms to the shape anddimensions of the Ni foam structure. The Ni foam is then etched awayusing an etching agent, leaving behind a monolith of graphene skeletonthat is essentially an open-cell foam. A useful reference for thismethod is given here: Zongping Chen, et al., “Three-dimensional flexibleand conductive interconnected graphene networks grown by chemical vapourdeposition,” Nature Materials, 10 (June 2011) 424-428. There are severalproblems associated with such a process: (a) the catalytic CVD isintrinsically a very slow, highly energy-intensive, and expensiveprocess; (b) the etching agent is typically a highly undesirablechemical and the resulting Ni-containing etching solution is a source ofpollution. It is very difficult and expensive to recover or recycle thedissolved Ni metal from the etchant solution. (c) It is challenging tomaintain the shape and dimensions of the graphene foam without damagingthe cell walls when the Ni foam is being etched away. The resultinggraphene foam is typically very brittle and fragile.

The third method of producing graphene foam also makes use of asacrificial material (e.g. colloidal polystyrene particles, PS) that iscoated with graphene oxide sheets using a self-assembly approach. Forinstance, Choi, et al. prepared chemically modified graphene (CMG) paperin two steps: fabrication of free-standing PS/CMG films by vacuumfiltration of a mixed aqueous colloidal suspension of CMG and PS (2.0 μmPS spheres), followed by removal of PS beads to generate 3D macro-pores.[B. G. Choi, et al., “3D Macroporous Graphene Frameworks forSupercapacitors with High Energy and Power Densities,” ACS Nano, 6(2012) 4020-4028.] Choi, et al. fabricated well-ordered free-standingPS/CMG paper by filtration, which began with separately preparing anegatively charged CMG colloidal and a positively charged PS suspension.A mixture of CMG colloidal and PS suspension was dispersed in solutionunder controlled pH (=2), where the two compounds had the same surfacecharges (zeta potential values of +13±2.4 mV for CMG and +68±5.6 mV forPS). When the pH was raised to 6, CMGs (zeta potential=−29±3.7 mV) andPS spheres (zeta potential=+51±2.5 mV) were assembled due to theelectrostatic interactions and hydrophobic characteristics between them,and these were subsequently integrated into PS/CMG composite paperthrough a filtering process.

The fourth method of producing a graphene foam (Aruna Zhamu and Bor Z.Jang, “Highly Conductive Graphene Foams and Process for Producing Same,”U.S. patent application Ser. No. 14/120,959 (Jul. 17, 2014); U.S.Publication No. 20160019995 (Jan. 21, 2016)) comprises:

(a) preparing a graphene dispersion having particles of an anode activematerial and a graphene material dispersed in a liquid medium, whereinthe graphene material is selected from pristine graphene, grapheneoxide, reduced graphene oxide, graphene fluoride, graphene chloride,graphene bromide, graphene iodide, hydrogenated graphene, nitrogenatedgraphene, chemically functionalized graphene, or a combination thereofand wherein the dispersion contains an optional blowing agent;(b) dispensing and depositing the graphene dispersion onto a surface ofa supporting substrate (e.g. plastic film, rubber sheet, metal foil,glass sheet, paper sheet, etc.) to form a wet layer of graphene-anodematerial mixture, wherein the dispensing and depositing procedureincludes subjecting the graphene dispersion to an orientation-inducingstress;(c) partially or completely removing the liquid medium from the wetlayer of graphene-anode material mixture to form a dried layer ofmaterial mixture having a content of non-carbon elements (e.g. 0, H, N,B, F, Cl, Br, I, etc.) no less than 5% by weight; and(d) heat treating the dried layer of material mixture at a first heattreatment temperature from 100° C. to 3,200° C. at a desired heatingrate sufficient to induce volatile gas molecules from the non-carbonelements or to activate the blowing agent for producing the anode layer.

The solid graphene foam in the anode layer typically has a density from0.01 to 1.7 g/cm³ (more typically from 0.1 to 1.5 g/cm³, and even moretypically from 0.1 to 1.0 g/cm³, and most typically from 0.2 to 0.75g/cm³), or a specific surface area from 50 to 3,000 m²/g (more typicallyfrom 200 to 2,000 m²/g, and most typically from 500 to 1,500 m²/g).

This optional blowing agent is not required if the graphene material hasa content of non-carbon elements (e.g. 0, H, N, B, F, Cl, Br, I, etc.)no less than 5% by weight (preferably no less than 10%, furtherpreferably no less than 20%, even more preferably no less than 30% or40%, and most preferably up to 50%). The subsequent high temperaturetreatment serves to remove a majority of these non-carbon elements fromthe graphene material, generating volatile gas species that producepores or cells in the solid graphene material structure. In other words,quite surprisingly, these non-carbon elements play the role of a blowingagent. Hence, an externally added blowing agent is optional (notrequired). However, the use of a blowing agent can provide addedflexibility in regulating or adjusting the porosity level and pore sizesfor a desired application. The blowing agent is typically required ifthe non-carbon element content is less than 5%, such as pristinegraphene that is essentially all-carbon.

In certain embodiments, the lithium ion-conducting porous structurecomprises a polymer foam or polymer fabric having pores and pore walls.The pore walls comprise a lithium ion-conducting polymer having alithium ion conductivity from 10⁻⁸ to 10⁻² S/cm when measured at 25° C.

In some embodiments, the lithium ion-conducting polymer is selected fromsulfonated polyaniline, sulfonated polypyrrole, a sulfonatedpolythiophene, sulfonated polyfuran, a sulfonated bi-cyclic polymer, ora combination thereof. These sulfonated polymers are found to be bothelectron-conducting and lithium ion-conducting.

In some embodiments, the lithium ion-conducting polymer contains asulfonated rubber or elastomer selected from sulfonated naturalpolyisoprene, sulfonated synthetic polyisoprene, sulfonatedpolybutadiene, sulfonated chloroprene rubber, sulfonatedpolychloroprene, sulfonated butyl rubber, sulfonated styrene-butadienerubber, sulfonated nitrile rubber, sulfonated ethylene propylene rubber,sulfonated ethylene propylene diene rubber, metallocene-based sulfonatedpoly(ethylene-co-octene) elastomer, sulfonated poly(ethylene-co-butene)elastomer, sulfonated styrene-ethylene-butadiene-styrene elastomer,sulfonated epichlorohydrin rubber, sulfonated polyacrylic rubber,sulfonated silicone rubber, sulfonated fluorosilicone rubber, sulfonatedperfluoroelastomers, sulfonated polyether block amides, sulfonatedchlorosulfonated polyethylene, sulfonated ethylene-vinyl acetate,sulfonated thermoplastic elastomer, sulfonated protein resilin,sulfonated protein elastin, sulfonated ethylene oxide-epichlorohydrincopolymer, sulfonated polyurethane, sulfonated urethane-urea copolymer,or a combination thereof.

In some embodiments, the lithium ion-conducting polymer is selected fromthe group consisting of poly(perfluoro sulfonic acid), sulfonatedpolytetrafluoroethylene, sulfonated perfluoroalkoxy derivatives ofpolytetra-fluoroethylene, sulfonated polysulfone, sulfonated poly(etherketone), sulfonated poly (ether ether ketone), sulfonated polystyrene,sulfonated polyimide, sulfonated styrene-butadiene copolymers,sulfonated poly chloro-trifluoroethylene, sulfonatedperfluoroethylene-propylene copolymer, sulfonatedethylene-chlorotrifluoroethylene copolymer, sulfonatedpolyvinylidenefluoride, sulfonated copolymers of polyvinylidenefluoridewith hexafluoropropene and tetrafluoroethylene, sulfonated copolymers ofethylene and tetrafluoroethylene, polybenzimidazole, and chemicalderivatives, copolymers, and blends thereof.

The production of sulfonation polymers is well-known in the art. One mayproduce a sulfonated polymer by polymerizing a sulfonated monomer or amonomer containing a sulfonyl group (e.g. T. G. Dang, et al. U.S.Publication No. 2005/0165213 (Jul. 28, 2005)). Preferably, one maysulfonate a polymer by immersing the polymer in a concentrated sulfuricacid (e.g. concentration >90%). For details one may consult C. J.Cornelius, et al. U.S. Pat. No. 7,301,002 (Nov. 27, 2007) and referencescited therein. In some embodiments, a desired polymer is made intofibers and then a fabric or paper structure, which is followed by asulfonation treatment. Alternatively, one may use a chemical blowingagent or physical blowing agent to assist in forming a polymer foamstructure (e.g. a film or sheet shape). The resulting porous structure(fabric, paper, or foam, etc.) may then be soaked with the lithiumion-capturing molecules or ionic salt solution discussed above.

In some embodiments, the lithium ion-conducting polymer is selected frompoly(ethylene oxide) (PEO), Polypropylene oxide (PPO),poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA),poly(vinylidene fluoride) (PVdF), Poly bis-methoxyethoxyethoxide-phosphazene, Polyvinyl chloride, Polydimethylsiloxane,and poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP) copolymer,modified polyacrylic acid-based copolymer, polyester polyamineamide-based copolymer, polycarboxylic acid-based copolymer, polyalkylolamino amide-based copolymer, polysiloxane polyacryl-based copolymer,polysiloxane polycarboxylic acid-based copolymer, polyalkoxylate-basedcopolymer, a copolymer of polyacryl and polyether, a derivative thereof,or a combination thereof. These materials can be readily made into aporous structure such as a fabric, paper, or foam structure.

There are several approaches that can be followed to form a lithium ionreservoir composed of a conducting framework porous structure (foam,paper, fabric, etc.) having pores filled with lithium ion-capturingmolecules or ions. It may be noted that these molecules or ions eitherhave a low melting point (lower than 100° C. or even <25° C.) and, thus,can be easily melted to become a highly flowable state, or can bedissolved in a liquid solvent to become solution. Hence, these lithiumion-capturing species can be readily made to permeate into pores of theporous framework structure. Such permeation can be accomplished byusing, for instance, the following procedures:

-   -   (a) Solution permeation: This includes dispersion or dissolution        of molecules or ions in water or a solvent to form a solution or        suspension, followed by coating or spraying the solution onto        the porous structure or by dipping the porous structure into        this solution or suspension; or    -   (b) Melt mixing: This includes bringing the molecules or ionic        species into a molten (liquid) state and allowing the liquid to        permeate into the pores of the porous structure using, coating,        spraying, dipping, etc.

Specifically, one may dispense and deposit a layer of the species in aliquid or solution state onto a primary surface of the porous structureusing air pressure-assisted spraying, ultrasonic spraying, casting,coating, and the like, preferably followed by a roll-pressing or othermeans of consolidating the lithium ion reservoir layer.

In the lithium-ion battery, the anode (sometimes referred to as anodeelectrode) typically is composed of an anode active material, aconductive additive (e.g. carbon black, acetylene black, graphiteplatelets, carbon nanotubes, etc.), and a resin binder (e.g. thewell-known SBR rubber, PVDF, CMC, etc.). In some embodiments, the anodeelectrode may comprise an anode active material comprising an elementselected from Si, Ge, Sn, Cd, Sb, Pb, Bi, Zn, Al, Co, Ni, Ti, or analloy thereof.

In some embodiments, the anode comprises an anode active materialselected from the group consisting of: (A) lithiated and un-lithiatedsilicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb),bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel (Ni),cobalt (Co), and cadmium (Cd); (B) lithiated and un-lithiated alloys orintermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co,or Cd with other elements; (C) lithiated and un-lithiated oxides,carbides, nitrides, sulfides, phosphides, selenides, and tellurides ofSi, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, Mn, V, or Cd, and theirmixtures, composites, or lithium-containing composites; (D) lithiatedand un-lithiated salts and hydroxides of Sn; (E) lithium titanate,lithium manganate, lithium aluminate, lithium-containing titanium oxide,lithium transition metal oxide; (F) lithiated and un-lithiated particlesof natural graphite, artificial graphite, mesocarbon microbeads, hardcarbon (commonly defined as the carbon materials that cannot begraphitized at a temperature higher than 2,500° C.), soft carbon (carbonmaterials that can be graphitized at a temperature higher than 2,500°C.), needle coke, polymeric carbon, carbon or graphite fiber segments,carbon nanofiber or graphitic nanofiber, carbon nanotube; andcombinations thereof.

The anode of a lithium-ion battery may be made by using the well-knownslurry coating method. For instance, one may mix particles of an anodeactive material (e.g. carbon-coated Si nanoparticles or nanowires), aresin binder (e.g. SBR rubber, CMC, polyacrylamide), and a conductivefiller (e.g. particles of acetylene black, carbon black, or carbonnanotubes) in water or an organic solvent (e.g. NMP) to form a slurry.The slurry is then coated on one primary surface or both primarysurfaces of a Cu foil and then dried to form an anode electrode. For theanode of a lithium metal battery, one may simply use a thin Li foilattached to a Cu foil or a graphene-based current collector.

The particles of an anode active material (e.g. Si, Ge, SiO_(x), Sn,SnO₂, etc., wherein x=0.01-1.9) preferably have a diameter from 5 nm to1 μm, more preferably from 10 to 500 nm, and most preferably from 20 to100 nm.

There is no restriction on the type of porous separator that can be usedin the presently invented lithium battery. A porous separator (e.g.polyolefin-based, non-woven of electrically insulating fibers, etc.) maybe used in lithium secondary batteries for the purpose of preventingshort circuiting between an anode and a cathode, but having poresserving as a passage for lithium ions. Most of the commerciallyavailable lithium batteries make use of a polyolefin (e.g. polyethylene,polypropylene, PE/PP copolymer, etc.) as a separator.

There is essentially no restriction on the type of cathode activematerials for use in the presently invented protected lithium cells. Thecathode active material in the cathode in this rechargeable alkali metalbattery may be selected from sulfur, selenium, tellurium, lithiumsulfide, lithium selenide, lithium telluride, sodium sulfide, sodiumselenide, sodium telluride, a chemically treated carbon or graphitematerial having an expanded inter-graphene spacing d₀₀₂ of at least 0.4nm, or an oxide, dichalcogenide, trichalcogenide, sulfide, selenide, ortelluride of niobium, zirconium, molybdenum, hafnium, tantalum,tungsten, titanium, vanadium, chromium, cobalt, manganese, iron, nickel,or a combination thereof. Preferred cathode active materials includenon-lithiated and slightly lithiated compounds having relatively highlithium or sodium storage capacities, such as TiS₂, MoS₂, MnO₂, CoO₂,and V₂O₅.

A novel family of 2D metal carbides or metal carbonides, now commonlyreferred to as MXenes, can be used as a cathode active material. MXenescan be produced by partially etching out certain elements from layeredstructures of metal carbides such as Ti₃AlC₂. For instance, an aqueous 1M NH₄HF₂ was used at room temperature as the etchant for Ti₃AlC₂.Typically, MXene surfaces are terminated by O, OH, and/or F groups,which is why they are usually referred to as M_(n+1)X_(n)T_(x), where Mis an early transition metal, X is C and/or N, T represents terminatinggroups (O, OH, and/or F), n=1, 2, or 3, and x is the number ofterminating groups. The MXene materials investigated include Ti₂CT_(x),(Ti_(0.5), Nb_(0.5))₂CT_(x), Nb₂CT_(x), V₂CT_(x), Ti₃C₂T_(x), (V_(0.5),Cr_(0.5))₃C₂T_(x), Ti₃CNT_(x), Ta₄C₃T_(x), and Nb₄C₃T_(x).

In an embodiment, the cathode layer contains an air cathode and thebattery is a lithium-air battery. In another embodiment, the cathodeactive material is selected from sulfur or lithium polysulfide and thebattery is a lithium-sulfur battery. In yet another embodiment, thecathode active material may be selected from an organic or polymericmaterial capable of capturing or storing lithium ions (e.g. viareversibly forming a redox pair with lithium ion).

In the cathode electrode of a lithium-ion battery, the cathode activematerial may be selected from a metaloxide/phosphate/sulfide/halogenide, an inorganic material, an organic orpolymeric material, or a combination thereof:

-   -   a) the group of metal oxide, metal phosphate, and metal sulfides        consisting of lithium cobalt oxide, lithium nickel oxide,        lithium manganese oxide, lithium vanadium oxide, lithium        transition metal oxide, lithium-mixed metal oxide (e.g. the        well-known NCM, NCA, etc.), transition metal fluoride,        transition metal chloride, lithium iron phosphate, lithium        manganese phosphate, lithium vanadium phosphate, lithium mixed        metal phosphates, transition metal sulfides, and combinations        thereof.        -   a. In particular, the lithium vanadium oxide may be selected            from the group consisting of VO₂, Li_(x)VO₂, V₂O₅,            Li_(x)V₂O₅, V₃O₈, Li_(x)V₃O₈, Li_(x)V₃O₇, V₄O₉, Li_(x)V₄O₉,            V₆O₁₃, Li_(x)V₆O₁₃, their doped versions, their derivatives,            and combinations thereof, wherein 0.1<x<5;        -   b. Lithium transition metal oxide may be selected from a            layered compound LiMO₂, spinel compound LiM₂O₄, olivine            compound LiMPO₄, silicate compound Li₂MSiO₄, tavorite            compound LiMPO₄F, borate compound LiMBO₃, or a combination            thereof, wherein M is a transition metal or a mixture of            multiple transition metals.    -   b) an inorganic material selected from: (a) bismuth selenide or        bismuth telluride, (b) transition metal dichalcogenide or        trichalcogenide, (c) sulfide, selenide, or telluride of niobium,        zirconium, molybdenum, hafnium, tantalum, tungsten, titanium,        cobalt, manganese, iron, nickel, or a transition metal; (d)        boron nitride, or (e) sulfur, sulfur compound, lithium        polysulfide (f) a combination thereof. In particular, TiS₂,        TaS₂, MoS₂, NbSe₃, non-lithiated MnO₂, CoO₂, iron oxide,        vanadium oxide, or a combination thereof may be used as a        cathode active material in a lithium metal cell.    -   c) the organic material or polymeric material may be selected        from poly(anthraquinonyl sulfide) (PAQS), a lithium oxocarbon,        3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),        poly(anthraquinonyl sulfide), pyrene-4,5,9,10-tetraone (PYT),        polymer-bound PYT, quino(triazene), redox-active organic        material, tetracyanoquinodimethane (TCNQ), tetracyanoethylene        (TCNE), 2,3,6,7,10,11-hexamethoxytriphenylene (HMTP),        poly(5-amino-1,4-dyhydroxy anthraquinone) (PADAQ), phosphazene        disulfide polymer ([(NPS₂)₃]n), lithiated        1,4,5,8-naphthalenetetraol formaldehyde polymer,        hexaazatrinaphtylene (HATN), hexaazatriphenylene        hexacarbonitrile (HAT(CN)₆), 5-benzylidene hydantoin, isatine        lithium salt, pyromellitic diimide lithium salt,        tetrahydroxy-p-benzoquinone derivatives (THQLi₄),        N,N′-diphenyl-2,3,5,6-tetraketopiperazine (PHP),        N,N′-diallyl-2,3,5,6-tetraketopiperazine (AP),        N,N′-dipropyl-2,3,5,6-tetraketopiperazine (PRP), a thioether        polymer, a quinone compound, 1,4-benzoquinone,        5,7,12,14-pentacenetetrone (PT),        5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ),        5-amino-1,4-dyhydroxy anthraquinone (ADAQ), calixquinone,        Li₄C₆O₆, Li₂C₆O₆, Li₆C₆O₆, or a combination thereof.        -   The thioether polymer is selected from            poly[methanetetryl-tetra(thiomethylene)] (PMTTM),            poly(2,4-dithiopentanylene) (PDTP), a polymer containing            poly(ethene-1,1,2,2-tetrathiol) (PETT) as a main-chain            thioether polymers, a side-chain thioether polymer having a            main-chain consisting of conjugating aromatic moieties, and            having a thioether side chain as a pendant,            poly(2-phenyl-1,3-dithiolane) (PPDT),            poly(1,4-di(1,3-dithiolan-2-yl)benzene) (PDDTB),            poly(tetrahydrobenzodithiophene) (PTHBDT),            poly[1,2,4,5-tetrakis(propylthio)benzene] (PTKPTB, or            poly[3,4(ethylenedithio)thiophene] (PEDTT).        -   The organic material may include a phthalocyanine compound            selected from copper phthalocyanine, zinc phthalocyanine,            tin phthalocyanine, iron phthalocyanine, lead            phthalocyanine, nickel phthalocyanine, vanadyl            phthalocyanine, fluorochromium phthalocyanine, magnesium            phthalocyanine, manganous phthalocyanine, dilithium            phthalocyanine, aluminum phthalocyanine chloride, cadmium            phthalocyanine, chlorogallium phthalocyanine, cobalt            phthalocyanine, silver phthalocyanine, a metal-free            phthalocyanine, a chemical derivative thereof, or a            combination thereof.

The cathode of a lithium-ion battery may be made by using the well-knownslurry coating method. For instance, one may mix particles of a cathodeactive material (e.g. particles of NMC, NCA, LiCoO₂, TiS₂,graphene-protected S particles, etc.), a resin binder (e.g. PVDF), and aconductive filler (e.g. particles of acetylene black, carbon black, orcarbon nanotubes) in an organic solvent (e.g. NMP) to form a slurry. Theslurry is then coated on one primary surface or both primary surfaces ofan Al foil and then dried to form a cathode electrode.

The electrolytes that can be used in the lithium battery may be selectedfrom any lithium metal salt that is dissolvable in a solvent to producean electrolyte. Preferably, the metal salt is selected from lithiumperchlorate (LiClO₄), lithium hexafluorophosphate (LiPF₆), lithiumborofluoride (LiBF₄), lithium hexafluoroarsenide (LiAsF₆), lithiumtrifluoro-metasulfonate (LiCF₃SO₃), bis-trifluoromethyl sulfonylimidelithium (LiN(CF₃SO₂)₂), lithium bis(oxalato)borate (LiBOB), lithiumoxalyldifluoroborate (LiBF₂C₂O₄), lithium oxalyldifluoroborate(LiBF₂C₂O₄), lithium nitrate (LiNO₃), li-fluoroalkyl-phosphates(LiPF₃(CF₂CF₃)₃), lithium bisperfluoro-ethysulfonylimide (LiBETI),lithium bis(trifluoromethanesulfonyl)imide, lithiumbis(fluorosulfonyl)imide, lithium trifluoromethanesulfonimide (LiTFSI),or a combination thereof.

The electrolytes used may contain a solvent selected from 1,3-dioxolane(DOL), 1,2-dimethoxyethane (DME), tetraethylene glycol dimethylether(TEGDME), poly(ethylene glycol) dimethyl ether (PEGDME), diethyleneglycol dibutyl ether (DEGDBE), 2-ethoxyethyl ether (EEE), sulfone,sulfolane, ethylene carbonate (EC), dimethyl carbonate (DMC),methylethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate,methyl propionate, propylene carbonate (PC), gamma-butyrolactone (γ-BL),acetonitrile (AN), ethyl acetate (EA), propyl formate (PF), methylformate (MF), toluene, xylene, methyl acetate (MA), fluoroethylenecarbonate (FEC), vinylene carbonate (VC), allyl ethyl carbonate (AEC), ahydrofluoroether, a room temperature ionic liquid solvent, or acombination thereof. The ionic liquid may also be used as an electrolytefor the lithium battery.

The anode of a lithium-ion battery may contain anode active materialparticles selected from the group consisting of: (a) silicon (Si),germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), zinc(Zn), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), andcadmium (Cd); (b) alloys or intermetallic compounds of Si, Ge, Sn, Pb,Sb, Bi, Zn, Al, Ti, Ni, Co, or Cd with other elements; (c) oxides,carbides, nitrides, sulfides, phosphides, selenides, and tellurides ofSi, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, V, or Cd, and theirmixtures, composites, or lithium-containing composites; (d) salts andhydroxides of Sn; (e) lithium titanate, lithium manganate, lithiumaluminate, lithium-containing titanium oxide, lithium transition metaloxide, ZnCo₂O₄; (f) particles of graphite and carbon; and (g)combinations thereof.

At the anode side, the anode active material of a lithium metal batterymay contain a layer of Li metal or alloy (>70% by weight of Li,preferably >80%, and more preferably >90%). Alternatively, the Li metalor alloy may be supported by a nanostructure composed of conductivenanofilaments. For instance, multiple conductive nanofilaments areprocessed to form an integrated aggregate structure, preferably in theform of a closely packed web, mat, or paper, characterized in that thesefilaments are intersected, overlapped, or somehow bonded (e.g., using abinder material) to one another to form a network of electron-conductingpaths. The integrated structure has substantially interconnected poresto accommodate electrolyte. The nanofilament may be selected from, asexamples, a carbon nanofiber (CNF), graphite nanofiber (GNF), carbonnanotube (CNT), metal nanowire (MNW), conductive nanofibers obtained byelectrospinning, conductive electrospun composite nanofibers, nanoscaledgraphene platelet (NGP), or a combination thereof. The nanofilaments maybe bonded by a binder material selected from a polymer, coal tar pitch,petroleum pitch, mesophase pitch, coke, or a derivative thereof.

Nanofibers may be selected from the group consisting of an electricallyconductive electrospun polymer fiber, electrospun polymer nanocompositefiber comprising a conductive filler, nanocarbon fiber obtained fromcarbonization of an electrospun polymer fiber, electrospun pitch fiber,and combinations thereof. For instance, a nanostructured electrode canbe obtained by electrospinning of polyacrylonitrile (PAN) into polymernanofibers, followed by carbonization of PAN. It may be noted that someof the pores in the structure, as carbonized, are greater than 100 nmand some smaller than 100 nm.

In summary, a possible lithium cell may be comprised of an alkali metallayer (e.g. Li foil, etc.) or an anode active material particle layer(e.g. particles of Si plus conductive additive and binder resin), ananode current collector (e.g. Cu foil and/or a nanostructure ofinterconnected conductive filaments) supporting the anode layer, alithium ion reservoir layer, a porous separator and an electrolytephase, a cathode, and an optional cathode current collector (e.g. Alfoil and/or or a nanostructure of interconnected conductive filaments,such as graphene sheets and carbon nanofibers) to support the cathodelayer. These layers may be laminated together to form a battery cell,followed by injection of a liquid electrolyte (if electrolyte is not yetincorporated in the laminate). The battery cell production proceduresare well-known in battery industry.

The following examples serve to illustrate the preferred embodiments ofthe present invention and should not be construed as limiting the scopeof the invention:

Example 1: Synthesis of Sulfonated Polyaniline (S-PANi)

The chemical synthesis of the S-PANi polymers was accomplished byreacting polyaniline with concentrated sulfuric acid. The procedure wassimilar to that used by Epstein, et al. (U.S. Pat. No. 5,109,070, Apr.28, 1992). The resulting S-PANi can be represented by the followingFormula 1, with R₁, R₂, R₃, and R₄ group being H, SO₃ ⁻ or SO₃H (R₅=H)with the content of the latter two being varied between 30% and 75%(i.e., the degree of sulfonation varied between 30% and 75%).

The lithium ion conductivity of these SO₃ ⁻ or SO₃H-based S-PANicompositions was in the range from 8.5×10⁻⁵ S/cm to 4.6×10⁻³ S/cm andtheir electron conductivity in the range from 0.1 S/cm to 0.5 S/cm whenthe degree of sulfonation was from approximately 30% to 75% (with ybeing approximately 0.4-0.6).

The porous framework for the lithium ion reservoir layer was obtained bydissolving S-PANi in water to form a polymer-water solution, which wasfreeze-dried to obtain a sponge-like foamed structure. A porosity levelfrom approximately 20% to 85% was achieved. Upon fully drying the foam,the pores in several foam structures were impregnated with severaldifferent lithium ion-capturing species, respectively: including lithium4-methylbenzenesulfonate, lithium aniline sulfonate, lithium sulfate,lithium phosphate, and an ionic liquid having a1-ethyl-3-methylimidazolium (EMI) cation and anN,N-bis(trifluoromethane)sulfonamide (TFSI) anion.

The resulting lithium ion-capturing reservoir layers were thenimplemented in several lithium cells, including lithium-ion cells(“graphite anode+NCA cathode” and “anode of graphene-protected Siparticles+NCM cathode”) and lithium metal cells (“Li metal foilanode+MoS₂ cathode” and “Li metal anode+graphene/S cathode).

We have observed that, by implementing a lithium ion reservoir betweenthe anode layer and the porous separator layer, one enables theresulting lithium-ion batteries or lithium metal batteries to befast-charged at a rate of 10 C to 30 C with only a 10% capacityreduction as compared to the battery measured at a rate of 0.5 C. Incontrast, when recharged at a high C rate (e.g. 10 C), the capacity ofthe conventional battery is less than 50% of the original capacitymeasured at 0.5 C rate.

Example 2: Sulfonation of Electrically Non-Conducting Polymers

Polytetrafluoroethylene (PTFE), polysulfone (PSf), poly (ether etherketone) (PEEK), polyimide (PI), and styrene-butadiene copolymers (SB)were separately immersed in a concentrated sulfuric acid (95%+5% water)at 65-90° C. for 4-48 hours to obtain sulfonated polymers. Thesesulfonated polymers were found to be electrically insulating (<10⁻⁸S/cm), but lithium ion-conducting (typically 3×10⁻⁵ S/cm-4.5×10⁻³ S/cm,depending on the degree of sulfonation).

These highly sulfonated polymers, along with some desired amounts ofbaking soda as a blowing agent, were dissolved in water to formsolutions, which were cast to form thin films onto a glass substrate andheated at 100° C.-250° C. for 0.3 to 5 minutes to produce porousstructures. In one additional sample, graphene oxide sheets(graphene/polymer ratio=1/10) were added to the sulfonated PEEK/bakingsoda solution to form a slurry, which was cast, dried, and heat-treatedat 300° C. for 5 minutes to obtain a graphene-enhanced S-PEEK foamstructure that was both electron-conducting and lithium ion-conducting.All these foamed structures were separately impregnated with lithiumaniline sulfonate or lithium sulfate to form lithium ion reservoirlayers.

Example 3: Preparation of Graphene Oxide Sheets (GO) and ReducedGraphene Oxide (RGO) Foam

Chopped graphite fibers with an average diameter of 12 μm and naturalgraphite particles were separately used as a starting material, whichwas immersed in a mixture of concentrated sulfuric acid, nitric acid,and potassium permanganate (as the chemical intercalate and oxidizer) toprepare graphite intercalation compounds (GICs). The starting materialwas first dried in a vacuum oven for 24 h at 80° C. Then, a mixture ofconcentrated sulfuric acid, fuming nitric acid, and potassiumpermanganate (at a weight ratio of 4:1:0.05) was slowly added, underappropriate cooling and stirring, to a three-neck flask containing fibersegments. After 5-16 hours of reaction, the acid-treated graphite fibersor natural graphite particles were filtered and washed thoroughly withdeionized water until the pH level of the solution reached 6. Afterbeing dried at 100° C. overnight, the resulting graphite intercalationcompound (GIC) or graphite oxide fiber was re-dispersed in water and/oralcohol to form a slurry.

In one sample, five grams of the graphite oxide fibers were mixed with2,000 ml alcohol solution consisting of alcohol and distilled water witha ratio of 15:85 to obtain a slurry mass. Then, the mixture slurry wassubjected to ultrasonic irradiation with a power of 200 W for variouslengths of time. After 20 minutes of sonication, GO fibers wereeffectively exfoliated and separated into thin graphene oxide sheetswith oxygen content of approximately 23%-31% by weight. The resultingsuspension contains GO sheets being suspended in water. A chemicalblowing agent (hydrazo dicarbonamide) was added to the suspension justprior to casting.

The resulting suspension was then cast onto a stainless steel plate. Awiper was used to exert shear stresses at a high shearing rate, inducingGO sheet orientations. The wet GO suspension was then dried. For makinga graphene foam specimen, the GO suspension was then subjected to heattreatments that typically involve an initial thermal reductiontemperature of 80° C.-350° C. for 1-8 hours, followed by heat-treatingat a second temperature of 1,500° C.-2,850° C. for 0.5 to 5 hours. Wehave found it essential to apply a compressive stress to the samplewhile being subjected to the first heat treatment. This compress stressseems to have helped maintain good contacts between the graphene sheetsso that chemical merging and linking between graphene sheets can occurwhile pores are being formed. Without such a compressive stress, theheat-treated sample was typically excessively porous with constituentgraphene sheets in the pore walls being very poorly oriented andincapable of chemical merging and linking with one another. As a result,the thermal conductivity, electrical conductivity, and mechanicalstrength of the graphene foam were compromised.

The resulting graphene foam structures were then separately dipped inseveral lithium ion-capturing species in a liquid state, includingsodium 4-methylbenzenesulfonate, sodium aniline sulfonate, sodiumsulfate, sodium phosphate, and an ionic liquid having atetra-alkylimidazolium cation and a BF₄ ⁻ anion, to prepare variouslithium ion reservoir layers.

Example 4: Preparation of Pristine Graphene Foam (0% Oxygen)

Recognizing the possibility of the high defect population in GO sheetsacting to reduce the conductivity of individual graphene plane, wedecided to study if the use of pristine graphene sheets (non-oxidizedand oxygen-free, non-halogenated and halogen-free, etc.) can lead to agraphene foam having a higher thermal conductivity. Pristine graphenesheets were produced by using the direct ultrasonication or liquid-phaseproduction process.

In a typical procedure, five grams of graphite flakes, ground toapproximately 20 μm or less in sizes, were dispersed in 1,000 mL ofdeionized water (containing 0.1% by weight of a dispersing agent, Zonyl®FSO from DuPont) to obtain a suspension. An ultrasonic energy level of85 W (Branson 5450 Ultrasonicator) was used for exfoliation, separation,and size reduction of graphene sheets for a period of 15 minutes to 2hours. The resulting graphene sheets are pristine graphene that havenever been oxidized and are oxygen-free and relatively defect-free.There are no other non-carbon elements.

Various amounts (1%-30% by weight relative to graphene material) ofchemical bowing agents (N, N-dinitroso pentamethylene tetramine or 4.4′-oxybis (benzenesulfonyl hydrazide) were added to a suspensioncontaining pristine graphene sheets and a surfactant. The suspension wasthen cast onto a glass surface using a doctor's blade to exert shearstresses, inducing graphene sheet orientations. Several samples werecast, including one that was made using CO₂ as a physical blowing agentintroduced into the suspension just prior to casting). The resultinggraphene suspension shapes, after removal of liquid, have a thicknessthat can be varied from approximately 0.1 mm to 50 mm.

The graphene shapes were then subjected to heat treatments that involvean initial (first) thermal reduction temperature of 80° C.-1,500° C. for1-5 hours. This first heat treatment generated a graphene foamstructure. Some of the pristine foam samples were then subjected to asecond temperature of 1,500° C.-2,850° C. to further perfect thegraphene foam structure (re-graphitized to become more ordered or havinga higher degree of crystallinity). These foam structures were used as aframework porous structure for accommodating lithium ion-capturingspecies.

Example 5: Lithium Ion-Conducting Polymer-Based Porous Structures

Another group of presently invented lithium ion-conducting frameworkporous structures to retain lithium ion-capturing species thereintypically comprises a mixture of a conventional lithium ion-conductingelectrolyte polymer (e.g. PEO, PPO, etc.) and a sulfonated polymer. Asshown in FIG. 2, the lithium ion conductivity values of a polymermixture containing a conventional solid electrolyte polymer (PEO or PPO)and a sulfonated polymer exhibit unexpected synergistic effect. Someelectron-conducting fillers (e.g. carbon nanotubes (CNF), carbonnanofibers (CNT), carbon black (CB), expanded graphite flakes (EGF),etc.) were added into lithium ion-conducting polymers to make a materialboth electron-conducting and lithium ion-conducting. Such a materialappears to be more effective in capturing lithium ions during the fastbattery charge operations, retaining more lithium ions in the resultingreservoir and continuing to send lithium ions into the anode layer evenafter the external charger unit is switched off.

TABLE 2 Lithium ion conductivity of various conducting framework porousstructure materials. Conducting Lithium-conducting CNTs or carbonpolymer Li-ion Sample fibers (CF), (non-sulfonated conductivity No. etc.particles polymer) (S/cm) D1 CNT + CB PEO 1.1 × 10⁻⁴ to (15-85% by wt.)8.5 × 10⁻⁴ S/cm D2 CNF PEO 2.3 × 10⁻⁴ to (5-95% by wt.) 8.2 × 10⁻⁴ S/cmD3 EGF PEO 2.3 × 10⁻⁴ to 7.2 × 10⁻⁴ S/cm D4 CNF + EGF PAN 6.5 × 10⁻⁵ to5.3 × 10⁻⁴ S/cm D5 CNF + graphene PPO 6.8 × 10⁻⁵ to 4.9 × 10⁻⁴ S/cm D6CNT + graphene PEO + S-PANi 5.9 × 10⁻⁴ to 7.7 × 10⁻³ S/cm D7 CNT PEO +S-PSf 3.4 × 10⁻⁴ to 1.3 × 10⁻³ S/cm

Example 6: Preparation of MoS₂/RGO Hybrid Cathode Material for Li MetalCells (GO=Graphene Oxide; RGO=Reduced Graphene Oxide)

Ultra-thin MoS₂/RGO hybrid was synthesized by a one-step solvothermalreaction of (NH₄)₂MoS₄ and hydrazine in an N, N-dimethylformamide (DMF)solution of graphene oxide (GO) at 200° C. In a typical procedure, 22 mgof (NH₄)₂MoS₄ was added to 10 mg of GO dispersed in 10 ml of DMF. Themixture was sonicated at room temperature for approximately 10 min untila clear and homogeneous solution was obtained. After that, 0.1 ml ofN₂H₄—H₂O was added. The reaction solution was further sonicated for 30min before being transferred to a 40 mL Teflon-lined autoclave. Thesystem was heated in an oven at 200° C. for 10 h. Product was collectedby centrifugation at 8000 rpm for 5 min, washed with DI water andrecollected by centrifugation. The washing step was repeated for atleast 5 times to ensure that most DMF was removed. Finally, product wasdried and made into a cathode.

The cathode layer, coated on an Al foil, was combined with a porousseparator, a lithium ion reservoir layer, and a lithium metal foil(supported by a Cu foil) to make a battery cell. The electrolyte usedwas a quasi-solid electrolyte (3.5 M of LiPF₆ in PC-EC solvent mixture).The resulting battery was found to be highly fire resistant whennail-penetrated.

Example 7: Preparation of Graphene-Enabled Li_(x)V₃O₈ Nanosheets as aCathode for a Li-Ion Cell

All chemicals used in this study were analytical grade and were used asreceived without further purification. V₂O₅ (99.6%, Alfa Aesar) and LiOH(99+%, Sigma-Aldrich) were used to prepare the precursor solution.Graphene oxide (GO, 1% w/v obtained from Taiwan Graphene Co., Taipei,Taiwan) was used as a structure modifier. First, V₂O₅ and LiOH in astoichiometric V/Li ratio of 1:3 were dissolved in actively stirredde-ionized water at 50° C. until an aqueous solution of Li_(x)V₃O₈ wasformed. Then, GO suspension was added while stirring, and the resultingsuspension was atomized and dried in an oven at 160° C. to produce thespherical composite particulates of GO/Li_(x)V₃O₈ nanosheets and thesample was designated NLVO-1. Corresponding Li_(x)V₃O₈ materials wereobtained under comparable processing conditions, but without grapheneoxide sheets. The sample was designated as LVO-2.

The Nyquist plots obtained from electrical impedance tests show asemicircle in the high to medium frequency range, which describes thecharge-transfer resistance for both electrodes. The intercept value isconsidered to represent the total electrical resistance offered by theelectrolyte. The inclined line represents the Warburg impedance at lowfrequency, which indicates the diffusion of ions in the solid matrix.The values of Rct for the vanadium oxide alone and graphene-enhancedcomposite electrodes are about 50.0 and 350.0Ω for NLVO-1 and LVO-2,respectively. The Rct of the composite electrode is much smaller thanthat of the LVO electrode. Therefore, the presence of graphene (<2% byweight in this case) in the vanadium oxide composite has dramaticallyreduced the internal charge transfer resistance and improved the batteryperformance upon extended cycling. NLVO-1 was subsequently used in twoLi-ion cells (one featuring a Li ion reservoir layer and the other not)for evaluation of the effect of a lithium ion reservoir layer on themaximum amount of charges that can be stored in the anode.

The NLVO-based cathode material was formed into a cathode and thencombined with a layer of lithiated natural graphite particles (as ananode), a lithium ion reservoir layer and a porous separator layer(Celgard 2400) to prepare a lithium-ion battery. A corresponding cellcontaining no lithium ion reservoir layer was also prepared forcomparison purpose. The electrolyte was a conventional PEO gelelectrolyte containing LiPF₆ in PC-EC solvent.

The capacity of both cells was designed to be approximately 500 mAh inthese two pouch cells. The actual charge storage capacity values ofthese two cells as a function of the charging C rates are summarized inFIG. 3, which clearly demonstrates the surprising effectiveness of thepresently invented lithium ion reservoir approach to maintaining a highcapacity at very high C rates.

Example 8: Relatively Fast-Chargeable Li—S Batteries

The cathode electrode was prepared following the following procedure.The electrochemical deposition of sulfur (S) was conducted before thecathode active layer was incorporated into a lithium-sulfur battery cell(Li—S). The anode, the electrolyte, and the integral layer of porousgraphene structure (serving as a cathode layer) are positioned in anexternal container outside of a lithium-sulfur cell. The neededapparatus was similar to an electroplating system, which is well-knownin the art.

In a typical procedure, a metal polysulfide (Li₂S₉ and Nai₂S₆) wasdissolved in a solvent (e.g. mixture of DOL/DME at a volume ratio from1:3 to 3:1) to form an electrolyte solution. The electrolyte solutionwas then poured into a chamber or reactor under a dry and controlledatmosphere condition (e.g. He or Nitrogen gas). A metal foil was used asthe anode and a layer of the porous graphene foam structure as thecathode; both being immersed in the electrolyte solution. Thisconfiguration constitutes an electrochemical deposition system. The stepof electrochemically depositing nanoscaled sulfur particles or coatingon the graphene surfaces was conducted at a current density preferablyin the range from 1 mA/g to 10 A/g, based on the layer weight of theporous graphene structure.

The chemical reactions that occurred in this reactor may be representedby the following equation: M_(x) S_(y)→M_(x)S_(y-z)+zS (typicallyz=1-4). Quite surprisingly, the precipitated S is preferentiallynucleated and grown on massive graphene surfaces to form nanoscaledcoating or nanoparticles. The coating thickness or particle diameter andthe amount of S coating/particles was controlled by the specific surfacearea, electrochemical reaction current density, temperature and time. Ingeneral, a lower current density and lower reaction temperature lead toa more uniform distribution of S and the reactions are easier tocontrol. A longer reaction time leads to a larger amount of S depositedon graphene surfaces and the reaction is ceased when the sulfur sourceis consumed or when a desired amount of S is deposited.

Several Li—S cells were produced wherein lithium metal foil was used asan anode active material and lithium trifluoromethane-sulfonimide(LiTFSI), dissolved in 1,3-dioxolane (DOL), was used as the electrolyte.In a first group of Li—S cells, a lithium ion reservoir layer obtainedin Example 1 was implemented between a porous PE-PP separator and alithium foil anode layer. In a second group of Li—S cells,graphene-reinforced sulfonated PEEK porous framework structure-basedlithium ion reservoir (containing lithium aniline sulfonate or lithiumphosphate as the lithium ion-capturing species), prepared in Example 2was implemented between the Li metal anode and the porous separator.Baseline Li—S cells containing no lithium ion reservoir were alsoprepared and tested for comparison.

It was observed that, the implementation of a lithium ion reservoirbetween the Li foil anode layer and the porous separator layer makes theresulting lithium-sulfur batteries fast-charged at a rate of 5 C to 15 Cwith only a 12-17% capacity reduction as compared to the same Li—Sbattery measured at a rate of 0.5 C. In contrast, when recharged at ahigh C rate (e.g. 10 C), the capacity of the baseline battery is reducedto become less than 50% of the original capacity measured at 0.5 C rate.

The discharge capacity values of two Li—S cells (each featuring a Lifoil as the anode active material and graphene-supported sulfur as thecathode active material) are plotted as a function of the number ofcharge/discharge cycles (FIG. 4). One cell contains a lithium ionreservoir disposed between the Li metal anode and the separator, but theother cell does not have such a reservoir. It is quite unexpected toobserve that the implementation of such a lithium ion reservoir layeralso results in a significantly more stable cycling behavior.Examination of post-cycling specimens led to the observation of asignificant amount of dead lithium particles separated from the lithiumfoil anode of the cell containing no lithium ion reservoir. In contrast,the lithium metal anode surface of the cell featuring a lithium ionreservoir appeared relatively smooth and very few dead Li particles wereobserved. Such a reservoir layer seems capable of helping to stabilizethe lithium metal-electrolyte interface zone and prevent dendriteformation, leading to a much longer cycle-life for a safer rechargeablelithium metal battery. Such a lithium ion reservoir strategy alsoenables the normally slow-charging lithium metal battery (including Li—Scell) to become fast chargeable.

The invention claimed is:
 1. A method of improving fast-chargeability ofa lithium secondary battery comprising an anode, a cathode, a porousseparator disposed between said anode and said cathode, and anelectrolyte, wherein said method comprises disposing a lithium ionreservoir between said anode and said porous separator and configured toreceive lithium ions from said cathode through said porous separatorwhen said battery is charged and to enable said lithium ions to entersaid anode in a time-delayed manner, wherein said lithium ion reservoircomprises a lithium ion-conducting porous framework structure havingpores, having a pore size from 1 nm to 500 μm, and lithium-capturinggroups residing in said pores, wherein said lithium-capturing groups areselected from (a) redox forming species that reversibly form a redoxpair with a lithium ion when said battery is charged; (b)electron-donating groups interspaced between non-electron-donatinggroups; (c) anions and cations wherein the anions are more mobile thanthe cations; or (d) chemical reducing groups that partially reducelithium ions from Li⁺¹ to Li^(+δ), wherein 0<δ<1, wherein said lithiumion-conducting porous structure comprises a polymer foam or polymerfabric having pore walls comprising a lithium ion-conducting polymerhaving a lithium ion conductivity from 10⁻⁸ to 10⁻² S/cm when measuredat 25° C., wherein said lithium ion conducting polymer comprises asulfonated polymer, wherein said sulfonated polymer is selected fromsulfonated polyaniline, sulfonated polypyrrole, a sulfonatedpolythiophene, sulfonated polyfuran, a sulfonated bi-cyclic polymer,sulfonated natural polyisoprene, sulfonated synthetic polyisoprene,sulfonated polybutadiene.
 2. The method of claim 1, wherein said lithiumion reservoir comprises an ionic liquid hosted by a porous structure. 3.The method of claim 1, wherein the lithium-capturing group is selectedfrom a molecule having a core or backbone structure and at least a sidegroup that contains an ionic or electron rich group; wherein the core orbackbone structure is selected from an aryl, heterocycloalkyl, crownetheryl, cyclamyl, cyclenyl, 1,4,7-triazacyclononayl, hexacyclenyl,cryptandyl, naphtalenyl, antracenyl, phenantrenyl, tetracenyl,chrysenyl, tryphenylenyl, pyrenyl, pentacenyl, single-benzene or cyclicstructure, double-benzene or bi-cyclic structure, or multiple-cyclicstructure having 3-10 benzene rings and wherein the side group comprisesCO₂H, CO₂M¹, CO₂R, SO₃H, SO₃M¹, PO₃H₂, PO₃M¹ ₂, PO₃M¹H, PO₄H₂, PO₄M¹ ₂,PO₄M¹H, PO₄M², C(O)NHOH, NH₂, NHR, N(R)₂, NO₂, COOR, CHO, CH₂OH, OH, OR,SH, SR, C(O)N(R)₂, C(O)NHR, C(O)NH₂, halide, tosylate, mesylate, SO₂NHR,triflate, isocyanate, cyanate, thiocyanate, isothiocyanate, R, cyano,CF₃, or Si(OR)₃; wherein R is independently selected from methyl, ethyl,isopropyl, n-propyl, alkyl, haloalkyl, cycloalkyl, heterocycloalkyl,aryl, or benzyl; M¹ is selected from Li, Na, K, Rb, or Cs; and M² isselected from Be, Mg, Ca, Sr, or Ba.
 4. The method of claim 1, whereinsaid redox pair with lithium is selected from the group consisting oflithium 4-methylbenzenesulfonate, lithium 3,5-dicarboxybenzenesulfonate,lithium 2,6-dimethylbenzene-1,4-disulfonate,3,3′-((1,2-dithiane-4,5-diyl)bis(oxy))bis(N-hydroxypropanamide),3,3′-((4-mercapto-1,2-phenylene)bis(oxy))bis(N-hydroxypropanamide),lithium aniline sulfonate, poly(lithium-4-styrenesulfonate, lithiumsulfate, lithium phosphate, lithium phosphate monobasic, lithiumtrifluoromethanesulfonate, lithium1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorooctane-1-sulfonate,lithium 2,6-di-tert-butylbenzene-1,4-disulfonate, lithium anilinesulfonate (wherein the sulfonate may be in any of para, meta and orthopositions), poly(lithium-4-styrenesulfonate, and combinations thereof.5. The method of claim 1, wherein said lithium ion-capturing groupcomprises a salt that is dissociated into an anion and a cation in aliquid medium wherein said salt is selected from the group consisting ofLi₂CO₃, Li₂O, Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂,(CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y), Na₂CO₃, Na₂O, Na₂C₂O₄, NaOH, NaX,ROCO₂Na, HCONa, RONa, (ROCO₂Na)₂, (CH₂OCO₂Na)₂, Na₂S, Na_(x)SO_(y), andcombinations thereof, wherein X=F, Cl, I, or Br, R=a hydrocarbon group,0<x≤1 and 1≤y≤4, and wherein said liquid medium to dissolve the saltcontains a solvent selected from the group consisting of 1,3-dioxolane(DOL), 1,2-dimethoxyethane (DME), tetraethylene glycol dimethylether(TEGDME), poly(ethylene glycol) dimethyl ether (PEGDME), diethyleneglycol dibutyl ether (DEGDBE), 2-ethoxyethyl ether (EEE), sulfone,sulfolane, ethylene carbonate (EC), dimethyl carbonate (DMC),methylethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate,methyl propionate, propylene carbonate (PC), gamma-butyrolactone (γ-BL),acetonitrile (AN), ethyl acetate (EA), propyl formate (PF), methylformate (MF), toluene, xylene, methyl acetate (MA), fluoroethylenecarbonate (FEC), vinylene carbonate (VC), allyl ethyl carbonate (AEC), ahydrofluoroether, hydrofluoro ether (FIFE), trifluoro propylenecarbonate (FPC), methyl nonafluorobutyl ether (MFE), fluoroethylenecarbonate (FEC), tris(trimethylsilyl)phosphite (TTSPi), triallylphosphate (TAP), ethylene sulfate (DTD), 1,3-propane sultone (PS),propene sultone (PES), diethyl carbonate (DEC), alkylsiloxane (Si—O),alkyylsilane (Si—C), liquid oligomeric silaxane (—Si—O—Si—),tetraethylene glycol dimethylether (TEGDME), an ionic liquid solvent,and combinations thereof.
 6. The method of claim 1, wherein said lithiumion-capturing groups comprise an ionic liquid having a cation selectedfrom the group consisting of tetra-alkylammonium, di-, tri-, ortetra-alkylimidazolium, alkylpyridinium, dialkyl-pyrrolidinium,dialkylpiperidinium, tetraalkylphosphonium, trialkylsulfonium, andcombinations thereof.
 7. The method of claim 1, wherein said lithiumion-capturing groups comprise an ionic liquid having an anion selectedfrom the group consisting of BF₄ ⁻, B(CN)₄ ⁻, CH₃BF₃ ⁻, CH₂CHBF₃ ⁻,CF₃BF₃ ⁻, C₂F₅BF₃ ⁻, n-C₃F₇BF₃ ⁻, n-C₄F₉BF₃ ⁻, PF₆ ⁻, CF₃CO₂ ⁻, CF₃SO₃⁻, N(SO₂CF₃)₂ ⁻, N(COCF₃)(SO₂CF₃)⁻, N(SO₂F)₂ ⁻, N(CN)₂ ⁻, C(CN)₃ ⁻,SCN⁻, SeCN⁻, CuCl₂, AlCl₄ ⁻, F(HF)_(2.3) ⁻, and combinations thereof. 8.The method of claim 1, wherein said lithium ion-capturing groupscomprise an ionic liquid having a 1-ethyl-3-methylimidazolium (EMI)cation and an N,N-bis(trifluoromethane)sulfonamide (TFSI) anion.
 9. Thelithium secondary battery of claim 1, wherein said pores comprisemesoscaled pores having a pore size from 2 nm to 50 nm.
 10. The methodof claim 1, wherein said lithium ion-conducting polymer furthercomprises a polymer selected from the group consisting of poly(ethyleneoxide) (PEO), polypropylene oxide (PPO), poly(acrylonitrile) (PAN),poly(methyl methacrylate) (PMMA), poly(vinylidene fluoride) (PVDF), polybis-methoxy ethoxyethoxide-phosphazene, polyvinyl chloride,polydimethylsiloxane, poly(vinylidene fluoride)-hexafluoropropylene(PVDF-HFP) copolymer, modified polyacrylic acid-based copolymer,polyester polyamine amide-based copolymer, polycarboxylic acid-basedcopolymer, polyalkylol amino amide-based copolymer, polysiloxanepolyacryl-based copolymer, polysiloxane polycarboxylic acid-basedcopolymer, polyalkoxylate-based copolymer, a copolymer of polyacryl andpolyether, a derivative thereof, and combinations thereof.
 11. Themethod of claim 1, wherein said anode comprises lithium metal or alithium metal alloy as an anode active material.
 12. The method of claim1, wherein said anode comprises an anode active material selected fromthe group consisting of: a) lithiated and un-lithiated silicon (Si),germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), zinc(Zn), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), andcadmium (Cd); b) lithiated and un-lithiated alloys or intermetalliccompounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co, or Cd withother elements; c) lithiated and un-lithiated oxides, carbides,nitrides, sulfides, phosphides, selenides, and tellurides of Si, Ge, Sn,Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, Mn, V, or Cd, and their mixtures,composites, or lithium-containing composites; d) lithiated andun-lithiated salts and hydroxides of Sn; e) lithium titanate, lithiummanganate, lithium aluminate, lithium-containing titanium oxide, lithiumtransition metal oxide; f) lithiated and un-lithiated particles ofnatural graphite, artificial graphite, mesocarbon microbeads, hardcarbon (carbon materials that cannot be graphitized at a temperaturehigher than 2,500° C.), soft carbon (carbon materials that can begraphitized at a temperature higher than 2,500° C.), needle coke,polymeric carbon, carbon or graphite fiber segments, carbon nanofiber orgraphitic nanofiber, carbon nanotube; and combinations thereof.
 13. Themethod of claim 1, wherein said anode comprises particles of an anodeactive material having a size from 10 nm to 1 μm.
 14. The method ofclaim 1, wherein said lithium secondary battery is a lithium-ionbattery, a rechargeable lithium metal battery, a lithium-sulfur battery,a lithium-selenium battery, or a lithium-air battery.
 15. A method ofimproving fast-chargeability of a lithium secondary battery comprisingan anode, a cathode, a porous separator disposed between said anode andsaid cathode, and an electrolyte, wherein said method comprisesdisposing a lithium ion reservoir between said anode and said porousseparator and configured to receive lithium ions from said cathodethrough said porous separator when said battery is charged and to enablesaid lithium ions to enter said anode in a time-delayed manner, whereinsaid lithium ion reservoir comprises a lithium ion-conducting porousframework structure having pores, having a pore size from 1 nm to 500μm, and lithium-capturing groups residing in said pores, wherein saidlithium-capturing groups are selected from (a) redox forming speciesthat reversibly form a redox pair with a lithium ion when said batteryis charged; (b) electron-donating groups interspaced betweennon-electron-donating groups; (c) anions and cations wherein the anionsare more mobile than the cations; or (d) chemical reducing groups thatpartially, reduce lithium ions from Li⁺¹ to Li^(+δ), wherein 0<δ<1,wherein said lithium ion-conducting porous structure comprises a polymerfoam or polymer fabric having pore walls comprising a lithiumion-conducting polymer having a lithium ion conductivity from 10⁻⁸ to10⁻² S/cm when measured at 25° C., wherein said lithium ion-conductingpolymer is selected from the group consisting of sulfonated polyaniline,sulfonated polypyrrole, a sulfonated polythiophene, sulfonatedpolyfuran, a sulfonated bi-cyclic polymer, and combinations thereof.